Merge pull request #511 from groldan/performance_improvements

Performance and database size improvements
@jj0hns0n  and @jdgarrett  confirmed this works.  Merging.
first attempt at a geogit map command.

The geogit map command displays a map of the indicated layer (e.g. geogit map roads).
Run it from inside geogit-console so the JMapFrame gets to show up, otherwise the
System.exit() call in geogit makes the program exit before.