Move edit-user-talk to messages
- Clear the newtalk flag when they mark all their edit-user-talk read.
- Remove the section caching system. It was designed to avoid performance problems with Flow messages, but now that standard talk pages are in 'messages', messages should be relatively common (alerts were already not cached by this).
- Minor cleanups to reflect that messages are not only Flow (and a typo fix in the Gruntfile).