Add ownership to channels and associated enhancements

This is a bit of a big one, so I want to get it open for discussion.

This PR fixes both #131 and #154 by introducing Cancan to manage authorization.  Channels are now owned by a user.  A user may only delete a channel they own, unless they are an admin.  Nobody may delete channel id=1.

As always, feedback/questions welcomed! :smiley_cat: