[Model Server] Migrate existing GLSP operations to be executed by a 'ModelServerAwareHandler'

[ndoschek]

• Migrate GLSPServer to a ModelServerGLSPServer
• Introduce a ModelServerAwareBasicOperationHandler as BasicOperationHandler
• Migrate existing operation handlers to extend ModelServerAwareBasicOperationHandler
• Make use of commands to update the model on the modelserver