Create MappingSets from MappingSetModelFactory

[ramidzkh]

Lorenz basically forces all MappingSets to be an instance of MappingSetImpl as there is no way to construct a MappingSet directly from a MappingSetModelFactory
Also, there are many occurrences where MappingSet.create() is called even though a MappingSetModelFactory is available

Proposed solution:

• Add a createMappingSet method to MappingSetModelFactory
• Make MappingSet.create(MappingSetModelFactory) use the model factory
• Call MappingSet.create(MappingSetModelFactory) or MappingSetModelFactory.createMappingSet() where possible (the three calls of create() in the MappingSet class don't use the existing MappingSetModelFactory)