added recursive and non-recursive check methods to constraint service

renamed ICompositionContext to IElementCompositionContext
replaced IRemovable with decomposition feature of IElementCompositor
fixed existing compositors

channel creation works on the model level, but not yet on the UI level

clean up => YELLOW

model constraint service implementation

added GEF editor base and edit part factory service

added IConnector extensions
implemented IConnectorService
cleanup => some YELLOW

added editor binding extension point and service

renamed model element handler interface and base implementation