MessageModel work pt1

(I'll re-title as WIP if so requested)

This should be ok to merge as nothing is horribly broken.

Done:

• Fetches the session that we want to open to bootstrap that
• Fetches the chat history for that session

Unimplemented features:

• LEFT OUTER JOIN sentq
• Any write operations on messages

WTFs:

• An empty message at the top of the chat session
• It's as if the messages get reversed somewhere between SQL and QML