Fixes #15179

And remove highlighting in web UI

Full circle from #8940

* Fix not publishing update of remote timeline

* fix @ missing

* if/unless to if/else

Regression from f371b32

Fix hashtag links always being lowercase

* Add silent column to mentions

* Save silent mentions in ActivityPub Create handler and optimize it

Move networking calls out of the database transaction

* Add "limited" visibility level masked as "private" in the API

Unlike DMs, limited statuses are pushed into home feeds. The access
control rules between direct and limited statuses is almost the same,
except for counter and conversation logic

* Ensure silent column is non-null, add spec

* Ensure filters don't check silent mentions for blocks/mutes

As those are "this person is also allowed to see" rather than "this
person is involved", therefore does not warrant filtering

* Clean up code

* Use Status#active_mentions to limit returned mentions

* Fix code style issues

* Use Status#active_mentions in Notification

And remove stream_entry eager-loading from Notification

* Do not push DMs into the home feed

* Show DMs column after sending a DM, if DMs column is not already shown

* Add conversations API

* Add web UI for conversations

* Add test for conversations API

* Add tests for ConversationAccount

* Improve web UI

* Rename ConversationAccount to AccountConversation

* Remove conversations on block and mute

* Change last_status_id to be a denormalization of status_ids

* Add optimistic locking

If media_attachments are not loaded, SQL query is the same, but
the #exists? method performs SQL query even if preloaded

* Store home feeds for 7 days instead of 14

Reduces workload for status fan-out to active followers

* Fix test for user model

* No need to re-require sidekiq plugins, they are required via Gemfile

* Add derailed_benchmarks tool, no need to require TTY gems in Gemfile

* Replace ruby-oembed with FetchOEmbedService

Reduce startup by 45382 allocated objects

* Remove preloaded JSON-LD in favour of caching HTTP responses

Reduce boot RAM by about 6 MiB

* Fix tests

* Fix test suite by stubbing out JSON-LD contexts

* Added a timeline for Direct statuses
* Lists all Direct statuses you've sent and received
* Displayed in Getting Started
* Streaming server support for direct TL

* Changes to match other timelines in 2.0

* Add structure for lists

* Add list timeline streaming API

* Add list APIs, bind list-account relation to follow relation

* Add API for adding/removing accounts from lists

* Add pagination to lists API

* Add pagination to list accounts API

* Adjust scopes for new APIs

- Creating and modifying lists merely requires "write" scope
- Fetching information about lists merely requires "read" scope

* Add test for wrong user context on list timeline

* Clean up tests

slightly optimized FanOutOnWriteService again

adjusted to allow choosing it, yet

FanOutOnWriteService. The only recipient-specific part on them
is reblogged/favourited. But since only newly created statuses
appear on them, it is safe to assume that both attributes would
be false

redis-backed "mentions" timeline as redundant (given notifications)

Fix #233, fix #268

Fix #289 - don't download avatar unless the URL is http/https
Fix #293 - reblog/reblogged is now boost/boosted

during Fan Out On Write to load less stuff into memory

Fetching atom extracted from FetchRemoteAccountService and FetchRemoteStatusService
into FetchAtomService. Mentions of the constant "http://activityschema.org/collection/public"
skipped as it's not a real URL/user.

as well as formatting of content