Description of problem:

The notification system should be improved. Ideally, these improvements would be along the lines of:

- System notifications: set/removed by admin, appear at the top of pages, can be "cleared" for a logged in session by the user, e.g.
[Zanata will be momentarily unavailable at 6pm AEST for maintenance]
user: ok, noted *clicks the x, notification goes away*

- Update notifications: should be a nice momentary, floating box because that's all the user cares to see, e.g. user clicks save, box shows "Settings Saved", count to 5, box goes away.

- Error notifications should be similar to the system notifications, but only in response to errors, and not removable for the current page