Remove support for global models

[augustearth]

The 'globel' model thing was sorta half baked from the beginning. The idea was that one could apply constraints to all elements (vertices and edges) that have a given label. For example, say two models, M1 and M2, have the concept of a person. Vertices in the graph would have the label 'Person'. A global model might require that all vertices in the graph with the label person, whether they were created through M1 or M2, might be forced to require a name property. Seems like something one might want to do. However, in practice, I have never used it. The whole issue of having element labels be the same though the element is modeled in two different places is thorny.

The motivation for removing this functionality is JanusGraph, which has some pretty cool schema features. Property, edge, and vertex labels can be explicitly modeled and used in indexes. In order for the machinery to work, labels should be unique. They are not unique in current Carnival. M1.PERSON and M2.PERSON will have the same label. Similarly, M1.NAME (a name property) and M2.NAME would have the same property key. In order to take advantage of underlying database indexing, distinct property keys and element labels are needed.

• Incorporate something unique from the model class in element labels
• Incorporate something unique from the model class in property keys