* 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
* Rewrite Atom generation from stream entries to use Ox instead of Nokogiri::Builder
StreamEntry is now limited to only statuses, which allows some optimization. Removed
extra queries on AccountsController#show. AtomSerializer instead of AtomBuilderHelper
used in AccountsController#show, StreamEntriesController#show, StreamEntryRenderer
and PubSubHubbub::DistributionWorker
PubSubHubbub::DistributionWorker moves n+1 DomainBlock query to PubSubHubbub::DeliveryWorker
instead.
All Salmon slaps that aren't based on StreamEntry still use AtomBuilderHelper and Nokogiri
* All Salmon slaps now use Ox instead of Nokogiri. No touch from status on account
