Refactored data registry.

  - renamed to repository
  - dataref to handle
  - made repository return workspace
  - javadocs and comment cleanup
using proper Iterators class
fixing constructor generics
added Cursors.first
updated Proj.reproject/transform to not modify geometry in place, and be explicit about in place modification
updated Memory driver to persist workspaces (by name) in global map
Updates to convert command.

- added filter and bbox parameters
- added test case
- made second argument optional, in which output dumped to stdout as GeoJSON
added SingleWorkspace for workspaces containing a single dataset