* Fix incorrect use of old WebUI paths
PR #16171 renamed some routes but missed some occurrences.
Without #16772, this leads to unreachable routes in those cases.
* Fix floating action button being displayed on statuses and compose screen
* Make the area to the left “Show Thread” also expand the toot in Web UI
* Clicking the left part of a conversation with the avatars now opens it in Web UI
* 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