[#4458] Updates in preparation for putting ActivityStream in prod.
Removed old follow and timeline controller methods (replaced by
ForgeActivity). Left the timeline html in the code since we may
want to reuse it in ForgeActivity. Left one activity creation
call in (happens when new ticket created) since it doesn't affect
the UI, and it'll be nice to have a little data gathered.
Updated activitystream.enabled config param name to match the
others.