extending the client model

I've been thinking about how best to extend the client model while retaining and adding clarity to the code and I believe the best approach would be by layers of subclasses. We've got a good start on a reasonably simple ModelObject.

The second layer would be to define classes like Rolon, Unit, JUnit, etc. Here we could define the inter-rolon navigational methods. The third layer then would add the RoleML compositional methods.

But today I want to focus on a set of simple administrative utilities, robustness, exception handling and all.