* Add validations to admin settings

- Validate correct HTML markup
- Validate presence of contact username & e-mail
- Validate that all usernames are valid
- Validate that enums have expected values

* Fix code style issue

* Fix tests

Fix #6856
Fix #6951

* Add instance-wide setting to disable profile directory

Fixes #9496

When the profile directory is disabled:
- The “discoverable” setting is hidden from users
- The “profile directory” link is not shown on public pages
- /explore returns 404

* Move Setting.profile_directory check to a before_action filter

Fix #3894

* Add default_settings class method to ScopedSettings

ScopedSettings was extended to use value of unscoped setting instead of
only using defaults set in config/settings.yml for selected settings.
This adds possibility for admins to set default values of users' settings,
for example default theme (as requested in #7092).

* Add ability to change an instance default theme

Closes #7092

* Add separate setting for sidebar text (site_short_description)

* Fix tests

* Redesign landing page (again)

* Move login form in small version to the right column

* Display closed registrations message

* Add site setting for the hero image

* Fix test

* Increase spacing, maximum width, change call to action section

* Add option to show only local toots in timeline preview
Right know, toots from all the known fediverse are shown in the main
page of an instance. That however doesn't reflect the instance itself.
With this option the admin may choose to display only local toots so
that users checking the instance get a better idea of internal
conversations.

* Fix issues pointed by codeclimate and eslint

* Add default message for community timeline

* Update pl.yml

* Add GET /api/v1/instance/peers API to reveal known domains

* Add GET /api/v1/instance/activity API

* Make new APIs disableable, exclude private statuses from activity stats

* Fix code style issue

* Fix week timestamps

* Add consumable invites

* Add UI for generating invite codes

* Add tests

* Display max uses and expiration in invites table, delete invite

* Remove unused column and redundant validator

- Default follows not used, probably bad idea
- InviteCodeValidator is redundant because RegistrationsController
  checks invite code validity

* Add admin setting to disable invites

* Add admin UI for invites, configurable role for invite creation

- Admin UI that lists everyone's invites, always available
- Admin setting min_invite_role to control who can invite people
- Non-admin invite UI only visible if users are allowed to

* Do not remove invites from database, expire them instantly

* Allow staff badge to change from setting to hidden

* i18n: Update Polish translation

* Add moderator role and add pundit policies for admin actions

* Add rake task for turning user into mod and revoking it again

* Fix handling of unauthorized exception

* Deliver new report e-mails to staff, not just admins

* Add promote/demote to admin UI, hide some actions conditionally

* Fix unused i18n

* Improve OpenGraph tags for about pages

* Add thumbnail admin setting

* Fix error

* Fix up

When a new user confirms their e-mail, bootstrap their home timeline
by automatically following a set of accounts. By default, all local
admin accounts (that are unlocked). Can be customized by new admin
setting (comma-separated usernames, local and unlocked only)

* Redesign the landing page, mount public timeline on it

* Adjust the standalone mounted component to the lacking of router

* Adjust auth layout pages to new design

* Fix tests

* Standalone public timeline polling every 5 seconds

* Remove now obsolete translations

* Add responsive design for new landing page

* Address reviews

* Add floating clouds behind frontpage form

* Use access token from public page when available

* Fix mentions and hashtags links, cursor on status content in standalone mode

* Add footer link to source code

* Fix errors on pages that don't embed the component, use classnames

* Fix tests

* Change anonymous autoPlayGif default to false

* When gif autoplay is disabled, hover to play

* Add option to hide the timeline preview

* Slightly improve alt layout

* Add elephant friend to new frontpage

* Display "back to mastodon" in place of "login" when logged in on frontpage

* Change polling time to 3s

* Remove best_in_place

* Replace best_in_place usage with rails helpers

* Move admin/settings#index to #edit action

* Remove click_to__edit from i18n

* Add render_views for admin/settings spec

* Add coverage for admin/settings#update

* Add coverage for admin/settings typecasting open_registrations setting

* Simplify how admin/settings finds the value for updating

* Rely on activerecord to not update a value that hasnt changed

* Add coverage for non-existent setting

* Use a constant for boolean settings

* Add Admin::BaseController to wrap admin area

Extracts the setting of the `admin` layout and verifying that users are admins
to a common base class for the admin/ controllers.

* Add basic coverage for admin/reports and admin/settings controllers

with YAML-defined defaults. Add admin page for editing global settings. Add "site_description"
setting that would show as a paragraph on the frontpage