6805 Refactor the SelectionNotificationService

Initial version of new Qt based SelectionNotificationService
class.

refs #6805
6805 Refactor the SelectionNotificationService

Adding SelectionNotificationFiles

refs #6805
RE 6805 Refactor SelectionNotificationService class

Added basic test that the singleton can be accessed and the
method to emit the signal can be called.

refs #6805
Merge branch 'feature/6805_refactor_SelectionNotificationService_class' into develop