WIP with CommitCommentEvents.
CommitCommentEvents are being saved properly.
Fix fixtures to work with STI.

It turns out fixtures don't really work that well with single table
inheritance. Rather than having a YAML file for each subclass, you
should just have a single YAML file for all of them.

It seems smart enough to know which table name to load them into, but
once you have multiple fixture files that lead into the same table,
things don't work out so well.
Merge branch 'commit-comment-events'

Conflicts:
	app/jobs/github_import_job.rb