Feature/tweet as hub

If you login to value01 and try to "sudo service fedmsg-tweet restart" you'll notice that its init script doesn't interact correctly with the daemon... the lockfile doesn't get cleaned up.  All our other daemons work correctly.

This is especially strange because fedmsg-tweet is just like all the other daemons in many respects.  Their init scripts are copy/pastes of one another.  They both use the same wrapper code in ``fedmsg/commands/__init__.py``.

One significant difference is that fedmsg-tweet runs its own ``for`` loop while the other daemons attach ``FedmsgConsumer``s to a moksha-hub, and run that hub.

This code makes fedmsg-tweet just like all the other daemons in that respect last respect.