* 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

in the background instead. Should fix delay where blocked person
can interact with blocker for a short time before background job
gets processed

background as well since it's a computationally expensive