Introduced ISelectionProvider interface for classes which should able to provide the Application's selection. Implemented these for ProjectExplorer and PipingCalculationsView so that the application selection is set once the view become active. Removed clearing the selection when ProjectExplorer gets disposed, as this is not the only selection provider. Related to Issue [WTI-756] git-svn-id: https://repos.deltares.nl/repos/WettelijkToetsInstrumentarium/trunk@4608 5a3db67b-de53-47b5-99c8-a1c30a6650e2