* Fix regeneration marker not being removed after completion

* Return HTTP 206 from /api/v1/timelines/home if regeneration in progress
Prioritize RegenerationWorker by putting it into default queue

* Display loading indicator and poll home timeline while it regenerates

* Add graphic to regeneration message

* Make "not found" indicator consistent with home regeneration

* Translated using Weblate (French)

Currently translated at 100.0% (56 of 56 strings)

Translation: Mastodon/Preferences
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/simple_form/fr/

* Translated using Weblate (Catalan)

Currently translated at 100.0% (56 of 56 strings)

Translation: Mastodon/Preferences
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/simple_form/ca/

* Translated using Weblate (Portuguese (Brazil))

Currently translated at 100.0% (260 of 260 strings)

Translation: Mastodon/React
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/frontend/pt_BR/

* Translated using Weblate (Portuguese (Brazil))

Currently translated at 100.0% (45 of 45 strings)

Translation: Mastodon/Devise
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/devise/pt_BR/

* Translated using Weblate (Dutch)

Currently translated at 100.0% (529 of 529 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/nl/

* Translated using Weblate (Dutch)

Currently translated at 100.0% (45 of 45 strings)

Translation: Mastodon/Devise
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/devise/nl/

* Translated using Weblate (Galician)

Currently translated at 100.0% (529 of 529 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/gl/

* Translated using Weblate (Galician)

Currently translated at 100.0% (45 of 45 strings)

Translation: Mastodon/Devise
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/devise/gl/

* Translated using Weblate (Portuguese (Brazil))

Currently translated at 99.6% (527 of 529 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/pt_BR/

* Translated using Weblate (Portuguese (Brazil))

Currently translated at 99.8% (528 of 529 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/pt_BR/

* Translated using Weblate (Portuguese (Brazil))

Currently translated at 100.0% (45 of 45 strings)

Translation: Mastodon/Devise
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/devise/pt_BR/

* Translated using Weblate (Portuguese (Brazil))

Currently translated at 100.0% (260 of 260 strings)

Translation: Mastodon/React
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/frontend/pt_BR/

* Translated using Weblate (Slovak)

Currently translated at 100.0% (56 of 56 strings)

Translation: Mastodon/Preferences
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/simple_form/sk/

* Translated using Weblate (Slovak)

Currently translated at 37.2% (197 of 529 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/sk/

* Translated using Weblate (Slovak)

Currently translated at 100.0% (260 of 260 strings)

Translation: Mastodon/React
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/frontend/sk/

* Translated using Weblate (Russian)

Currently translated at 99.0% (526 of 531 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/ru/

* Translated using Weblate (Catalan)

Currently translated at 100.0% (45 of 45 strings)

Translation: Mastodon/Devise
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/devise/ca/

* Translated using Weblate (Catalan)

Currently translated at 99.8% (530 of 531 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/ca/

* Translated using Weblate (Japanese)

Currently translated at 92.8% (52 of 56 strings)

Translation: Mastodon/Preferences
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/simple_form/ja/

* Translated using Weblate (Japanese)

Currently translated at 75.8% (47 of 62 strings)

Translation: Mastodon/Devise
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/devise/ja/

* Translated using Weblate (Polish)

Currently translated at 77.4% (48 of 62 strings)

Translation: Mastodon/Devise
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/devise/pl/

* Translated using Weblate (Slovak)

Currently translated at 38.3% (204 of 532 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/sk/

* Translated using Weblate (Japanese)

Currently translated at 100.0% (62 of 62 strings)

Translation: Mastodon/Devise
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/devise/ja/

* Translated using Weblate (Catalan)

Currently translated at 100.0% (62 of 62 strings)

Translation: Mastodon/Devise
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/devise/ca/

* Translated using Weblate (Polish)

Currently translated at 100.0% (62 of 62 strings)

Translation: Mastodon/Devise
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/devise/pl/

* Translated using Weblate (Polish)

Currently translated at 100.0% (75 of 75 strings)

Translation: Mastodon/Doorkeeper
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/doorkeeper/pl/

* Translated using Weblate (Polish)

Currently translated at 100.0% (62 of 62 strings)

Translation: Mastodon/Devise
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/devise/pl/

* Translated using Weblate (Polish)

Currently translated at 100.0% (56 of 56 strings)

Translation: Mastodon/Preferences
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/simple_form/pl/

* Translated using Weblate (Russian)

Currently translated at 96.8% (525 of 542 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/ru/

* Translated using Weblate (Japanese)

Currently translated at 99.0% (537 of 542 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/ja/

* Translated using Weblate (Polish)

Currently translated at 99.8% (541 of 542 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/pl/

* Translated using Weblate (Japanese)

Currently translated at 99.0% (538 of 543 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/ja/

* Translated using Weblate (Dutch)

Currently translated at 97.4% (529 of 543 strings)

Translation: Mastodon/Backend
Translate-URL: https://weblate.joinmastodon.org/projects/mastodon/backend/nl/

* Normalize translations
Ran i18n-tasks normalize && yarn manage:translations

* i18n: (zh-CN) Update translation for #6252

* e-mail -> email

* i18n: (zh-CN) Update translations for #6256

* i18n: (zh-CN) Minor Improvements

* i18n: (zh-CN) Update translations for #6263

* i18n: (zh-CN) Update translations for #6279

* HTML e-mails for NotificationMailer (except digest)

* Add HTML template for digest

* Fix build

- premailer gem to turn CSS into inline styles automatically
- rework UserMailer templates
- reword UserMailer templates

* Fix #1095 - Surround mid-text display names with bdi tags

* Update jest snapshot

* Add aria-autocomplete='list' in Textaria

ref: https://www.w3.org/TR/wai-aria-1.1/#aria-autocomplete

* Make detect empty string brefore assign upload description

* Change code elements in keyboard-shortcuts component to kbd

* Add validation for onMuteNotifications

* Make columns-area unscrollable when modal opend

* Make columns-area unscrollable when modal opened

* Fix accessibility of column headers

As a screen reader user new to Mastodon, I encountered the following issues with the column headers as designed:
 * Jumping between them was difficult. FOr instance, passing my home timeline to reach notification settings was difficult to impossible, especially considering infinite scrolling.
 * There doesn't appear to be any means for triggering the control via the keyboard. the `titleClick` handler only responds to mouse clicks.
 * I didn't even realize there was a Settings toggle until I made this change.

Thanks for using ARIA in your designs. It's a huge help. But adding a `button` role doesn't add keyboard handling and other button behavior. Also, because the role was on the heading container, it obscured the controls within the container itself. This fix resolve that. It also exposes the headings as headings rather than buttons, enabling skipping columns by using screen readers' heading navigation commands.

Since I myself am blind, if this fix requires additional visual styling, I'd like help applying that so it can be merged. I'd consider it an essential accessibility fix for my and other blind users' existence on the platform. Thanks!

* Styling fixes

* Fixed overflow issue

This makes the clickable element an interactive element, but doesn't add
alt text and makes it not-obvious that you can click the elefriend.  On
one hand, this goes against good practice; on the other hand, it's not
*supposed* to be obvious that you can click the elefriend.

Also lay some groundwork needed to interactively change the
glitchfriend.

The codebase uses "elefriend" because it's shorter and didn't require me
to realign the actions in actions/compose.js.  Same idea, though.

Glitched elephant friends kindly provided by @ncls7615.

Signed-off-by: Marcin Mikołajczak <me@m4sk.in>