Fixes #13882

Fix #9031
Fix #7913

* Add option to disable blurhash previews

* Update option text

* Change options order

* Add responsive panels to the single-column layout

* Fixes

* Fix not being able to save the preference

* Fix code style issues

* Set max-height on the compose textarea and add a link to relationship manager

* Make storing and displaying application used to toot opt-in

* Revert to storing application info, and display it to the author via API

* Add setting to not aggregate reblogs

Fixes #9222

* Handle cases where user is nil in add_to_home and add_to_list

* Add hint for setting_aggregate_reblogs option

* Reword setting_aggregate_reblogs label

* Allow selecting default posting language instead of auto-detect

* Enable default language setting in credentials API

* Fix form saving

* Add preference to hide following/followers lists

- Public pages
- ActivityPub collections (does not return pages but does give total)
- REST API (unless it's your own) (does not federate)

Fix #6901

* Add preference

* Add delegation

* Fix issue

* Fix issue

* Enable updating additional account information from user preferences via rest api
Resolves #6553

* Pacify rubocop

* Decoerce incoming settings in UserSettingsDecorator

* Create user preferences hash directly from incoming credentials instead of going through ActionController::Parameters

* Clean up user preferences update

* Use ActiveModel::Type::Boolean instead of manually checking stringified number equivalence

* Add option to reduce motion

* Use HOC to wrap all Motion calls

* fix case-sensitive issue

* Avoid updating too frequently

* Get rid of unnecessary change to _simple_status.html.haml

* Separate notifications preferences from general preferences

* Refine settings/notifications/show

* remove preferences.notifications

* Add support for selecting a theme

* Fix codeclimate issues

* Look up site default style if current user is not available due to e.g. not being logged in

* Remove outdated comment in common.js

* Address requested changes in themes PR

* Fix codeclimate issues

* Explicitly check current_account in application controller and only check theme availability if non-nil

* codeclimate

* explicit precedence with &&

* Fix code style in application_controller according to @nightpool's suggestion, use default style in embedded.html.haml

* codeclimate: indentation + return

* Add unfollow modal

* unfollowing someone

* remove unnecessary prop

* add a system_font_ui setting on the server

* Plug the system_font_ui on the front-end

* add EN/FR locales for the new setting

* put Roboto after all other fonts

* remove trailing whitespace so CodeClimate is happy

* fix user_spec.rb

* correctly write user_spect this time

* slightly better way of adding the classes

* add comments to the system-font stack for clarification

* use .system-font for the class instead

* don't use multiple lines for comments

* remove trailing whitespace

* use the classnames module for consistency

* use `mastodon-font-sans-serif` instead of Roboto directly

* Set delete_modal preference to true by default
* Does not show confirmation modal if delete_modal is false
* Add ja translation for preference setting page

* Add missing fields group on preferences page

* Clean up settings/preferences controller

* Extract a UserSettingsDecorator