Changeset discussion feature

New ChangesetComment model and join table between users and changsets for comments subscriptions
Made commeting changesets possible via "browse" interface
Comments feed for all changsets, particular changeset
Email notifications of new comments on "subscribed to" changesets
I know, but I was never very happy with it... The really crazy thing is that I don't think it's actually used anymore, but it was needed for the original notes implementation on the web site.