API refinements, DRM developments

Took most of the day off, but still managed to get some good work done this evening.

In the common package, two new interfaces have been added: IRolonicElement and IEntry. And in the DRM, I've now added SectionModel, EntryModel, ChildrenModel and MyKeywordsModel. I also dropped a number of inappropriate methods from the common interfaces and added a number of missing methods to the DRM.

I figure another day of API cleanups and then another day or two of documentation and then I can finally get back to working on queries and RoleML script.