WIP: Notifications in Navbar

Closes #151 

Works on the `notifier` service, that has been around for a while, but dormant.

We had a `NotifierCtrl` before - this is gone now. Messages are displayed by directives only.
The navbar is still the place to hold them. A configuration section has been added to configure the notifier - the max number of messages kept can be configured, as well as a duration that determines how long notifications stay up on the screen. Both come with sensible default values - it's not a necessity to include a notifier section in the configuration file.

Still WIP: A message menu that displays the archived messages.


Specs for the notifier service are included.