Connect to irc servers' channels on startup

These should have a flag to indicate whether or not they should
be autojoined
Fix data model for server's channels

Man, what a nightmare. I set the ParentEntity on Channel to Server
at some point, and that was a mistake. That resulted in a lot of
weird looking records being saved because that property actually
is for inheritance, not for relations.

Now channels are optional on server, but hostname, port, etc are
all required. Name is required on channel and so is the server.
Join servers on startup

Finally.
Fixup default channels

This begs the question, you should let users not join any channels at all?