RE 6805 Refactor SelectionNotificationService class

Removed original SelectionNotificationService .h, .cpp and
Test files from Framework/API/, since they have been replaced
by similarly named files using Qt signals and slots
in MantidQt/API/.

refs #6805
RE 6805 refactor SelectionNotificationService class

Fixed error in MantidQt/API/CMakeLists.txt, as suggested
by Russell.
Added basic test of SelectionNotificationService.

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