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 view icons on navigator and library.
Added editor-dependent filter for library view.

fixed base.project remove warnings builder id
fixed remove warnings builder id in .project files

Added saveable support to navigator

completed working undo/redo mechanism
fixed global actions update in navigator