Get chats out of mysql when loading the chat page.
New archive/delete configuration.

- Saved/group chats are archived to mysql periodically. If everyone has left the chat when the archiving happens, it's deleted from redis.
- Unsaved chats are deleted from redis shortly after the last person leaves, without ever touching mysql.
- Unsaved chats are automatically saved when the chat reaches 10 lines.
Remove the backlog option from archive_chat.

Just move the entire text to mysql every time.