Use server-side followup formatting in chat.

Change-Id: I4f6f01bb0f7fbb3fcebc0a9909610767ff2a6fc9
Re-enable chat PMs by default.

They were always enabled in ringhunters anyway, and ringhunters is the
biggest performance issue.  So it doesn't make much sense to disable
them elsewhere (but we can revisit this after loadtesting).

Change-Id: I721dd1d668dad5b9020c61a47234c2f386cd362b