element model release 10.0.0, goals for 11

New validate utility checks the integrity of a database.
Additional convenience methods added to AbstractApplication.
Javadoc rewritten for the elementmodel package.

This completes basic persistence. For release 11 there are 3 objectives:
- Employ weak references (in handles) and a cache to reduce the memory footprint.
- Use variable-length blocks in place of fixed-length blocks.
- Extend browse to the point where it operates as a simple wiki.