* Federate pinned statuses over ActivityPub

* Display pinned toots in web UI

Fix #6117

* Fix migration

* Fix tests

* Update outbox_serializer.rb

* Update remove_serializer.rb

* Update add_serializer.rb

* Update fetch_featured_collection_service.rb

- Objects must have attributedTo instead of actor
- The current attribute belongs to CollectionPage, not Collection

* Improve webfinger templates and make tests more flexible

* Clean up AS2 representation of actor

* Refactor outbox

* Create activities representation

* Add representations of followers/following collections, do not redirect /users/:username route if format is empty

* Remove unused translations

* ActivityPub endpoint for single statuses, add ActivityPub::TagManager for better
URL/URI generation

* Add ActivityPub::TagManager#to

* Represent all attachments as Document instead of Image/Video specifically
(Because for remote ones we may not know for sure)

Add mentions and hashtags representation to AP notes

* Add AP-resolvable hashtag URIs

* Use ActiveModelSerializers for ActivityPub

* Clean up unused translations

* Separate route for object and activity

* Adjust cc/to matrices

* Add to/cc to activities, ensure announce activity embeds target status and
not the wrapper status, add "id" to all collections