Add function calls to MdModules to sign up for notifications

Add function calls to MdModules to sign up for notifications

Allow MdModules to sign up to notifications after they know their own
options. This makes it possible that modules only get called back when
they need to and not by default and skips the if(active) logic in
functions that are called back in favour of not subscribing to the
notifications to begin with.

refs #3076

Change-Id: Ib95c1f734f919805c661ac6f6451af5da8187eec