Minor changes to ecore, plugin.xml, regenerated EMF model classes.
The biggest problem was that MyModelResourceFactoryImpl must extend
Bpmn2ModelerResourceFactoryImpl and createResource(URI) must return
a Bpmn2ModelerResourceImpl or some subclass of it.
Merge pull request #1 from bbrodt/bob-fixes

Minor changes to ecore, plugin.xml, regenerated EMF model classes.