This commit does a few things:
1) Add replies to messages, which are calculated at query time using a
join
2) Add a BlockContact api call that takes care of deleting messages from
a user, deleting the chat, and re-compute the denormalized values. As it
needs to run in a transaction, the method that it relies on take a
transaction as an optional parameter.
3) Change ID scheme for chats/contacts so that it's consistent across
messages/contacts
This is not compatible as I have modified a migration, but it's not a
problem as data compatibility can be broken