This introduces a new per-user preference called
"Auto-play animated GIFs", which is enabled by default. When a
user disables this setting, gifs in toots become click-to-play.

Previews of animated gifs were changed to display the video play
button so that users can distinguish them from regular images.

This setting also affects account avatars in the detailed account
view, which was changed to use the same hover-to-play mechanism
that is used for animated avatars in timelines.

Fixes #1652

* Fix #1870 - Strip control characters out of strings in AtomSerializer

* Adjust according to comment by @alpaca-tc

* Add language detection via WhatLanguage and (de)serialization of it through Atom

* Fix default language in ProcessFeedService

* Re-add newline before 'react-rails' Gem to fix groupings

Fixes Code Climate issue

* Basic onboarding modal that's shown to users once

* Lay out pages 2 through 5, add images, style modals (#1509)

* Lay out pages 2 through 5

Added images and laid out pages 2 through 5 in the jsx file. SCSS will
come, still working on just seeing if this works at all.

* Fix jsx errors, add images to modal pages, style modal pages

* Add animations to onboarding pager changes, improve wording and styling

* Finishing touches on the onboarding

* Add missing propTypes

* Update wording

* update Dockerfile: latest nodejs LTS

* also update imagemagick

* Rename admin.domain_block to admin.domain_blocks in prep for i18n improvement

* Use implicit controller/action path for i18n in admin/domain_blocks

* Add DomainBlock#accounts has_many

* Avoid i18n health warning for `en` locale by using symbol scope with :count

* Remove unused i18n key: plaintext_secret_html

* Remove unused i18n key two_factor_auth.warning

* Remove final will_paginate i18n keys

* Remove unused key two_factor_auth.recovery_codes

* Remove unused key: admin.reports.comment.none

* Remove unused reports. i18n namespace (moved to admin.reports)

* Ignore keys from locales which override activemodel and activerecord errors

* Revert "Remove unused key: admin.reports.comment.none"

This reverts commit 350ef2685fadc069e619bb6d1066190de195d942.

* Update i18n key reference to match moved location

* Add missing `en` keys to i18n

* Tell i18n-tasks to ignore missing attributes that dont need overwriting

* Add i18n-tasks unused to travis

The <link rel="mentioned" /> tag refers to accounts by href. So we were
matching the DB by the url attribute, and falling back to HTTP look-up.
However, GS and Mastodon use profile URLs as URIs, too, and the match
for that was missing. This could potentially alleviate some extra network
requests

* Adds note for instance admins.

* Addresses feedback from #1925.

* Use local vars in accounts/header partial

* Use local variable in 2fa recovery codes partial

* fix regex filter

* fixed br to linebreak and, stlip tags.

* change to send raw content

* changed to unescape in reducer

```
*An* `ActiveRecord::StatementInvalid` *occurred while* `POST </settings/import>` *was processed by* `imports#create`
Exception
----------------
PG::NotNullViolation: ERROR:  null value in column "type" violates not-null constraint
```

And `i18n-tasks add-missing -l ja` changes some quotes.

* Improve PT locale on simple_form

* Add missing keys to PT locale

* Fix yaml parse issue in ja.yml locale

* Fix issue in locales/ja.jsx

assets:precompile was failling because of this missing comma.

* Add missing french translation.

Causing this error:
[React Intl] Missing message: "navigation_bar.mutes" for locale: "fr",

* Update fr.jsx

* [Update ja.jsx] Add Muted, Video_error and sorted

* [Update ja] Added Recovery code's translation

* [Update ja] Added Two-fact/Recovery's translation

* Update ja.jsx

* Unite all mandatory rake tasks in mastodon:daily
Add mastodon:media:remove_remote task
Make mastodon:maintenance:add_static_avatars more resilient to exceptions

* Fix typo in task description