Replace EMF-based Model Extensions with new framework

Designer's current Model Extensions framework has some limitations which include:
1. The current framework allows for only 1 extension model.
2. Extension models are included as a dependent models in VDBs.
3. When sequenced through publishing into the Modeshape repository none of the default "extended" property values are currently sequenced. There is no mechanism in Modeshape to associate 2 or more documents in this way.
4. When using the EMF Extension Model, EMF controls when Annotation objects are created, and we're creating annotation objects even when none are strictly needed (e.g., all the tags in the annotation have default values, and thus don't appear in the XMI file). The result is a lot of unnecessary Annotation objects.

Need to design a new framework that is scalable, allows for applying multiple extensions, includes the extension metadata within a model (initial values and types) and can be easily adapted/sequenced by Modeshape.