Reintroduce Message List Model

Now both the old implementation and new is working side-by-side and it's
perfect.
New chats open instantly.
Switching between chats in chats view is instant as well.
Reduce time of loading a chat with messages.
Displays only messages from current session, older are available in
archive view (I can add an option to load them if anyone cares).
No UI lag when receiving messages.

It. Feels. AWESOME!