Provide Graphical DND for Class, Composite Structure, Package et State Machine diagrams

The tool must provide graphical DnD for Class, Composite Structure, Package et State Machine diagrams.

For Package and CompositeStructure the classes to used already exist in the domain-service, they have been developped for the Papyrus-Sirius Desktop version.

Concerning the Class and the Statemachine diagram, the required classes must be created in the domainservice, because this behavior is not yet implemented too for these diagrams in the Papyrus-Sirius Desktop version.