Don't crash when /part ing a channel
Better support for per-tab chats

Broke sending and receiving private messages.
Pull CoreData managed object context off App Delegate

Kept thinking about how complete insane this is. I suspect
it will be better if the interface is static, but this
should get us 90% of the way there.

The reason you wouldn't want to have this on the application
delegate is because anything that needs to save a record is
going to end up #importing the app delegate header, and likely
causing circular includes in the process.
Include channel / server properties on the models
Save IRC servers when connecting, not when connected

Small difference, but I don't know why you would want to
wait to save this record.
Display an error for invalid /who requests