UCM — enable extension for composite component implementation

It would be nice to allow a composite component implementation to extend another one. This can be achieved by adding a field extends to the existing CompositeComponentImplementation class. Composite extensions would allow the declaration of additional assembly parts, port delegations, attribute delegations and connections without altering the elements declared in ancestor components.

add composite component implementation refinement and update field names for extension mechanisms

Add a field extends in class CompositeComponentImplementation. Also add a field refines in classes AssemblyPart and Connection. Rename fiels instanceOf of class AssemblyPart into componentDefinition, as an assembly part is not an instance.
Fix inconsistencies in field names