The portion after StartAtomPubNewActivity would never be reached since
Favorite handles that activity through ActivityHandlerPlugin nowadays.
So I cleaned it up and followed a couple of paths, making stuff prettier.
The code is now more event-driven when it comes to rendering notices
and their related HTML elements, since we can't have direct calls from
core to a plugin.
lib/activitymover.php has a function to move a Favorite activity which
will not happen now. The move must be pluginified and performed as an
event which plugins can catch on to.
