Remove workaround for obtaining SRID

The fix for the missing SRID problem has been merged into GeoTrellis
Merge pull request #172 from WorldBank-Transport/feature/remove-srid-workaround

Remove workaround for obtaining SRID
Calculate, save stops buffer in database -untested

This adds a trait that allows indicators to calculate a stops buffer and
save it to the database. The current stops buffer in the database will
be retrieved if it already exists. This is untested code.
Add 500m coverage ratio indicator
Add StopsBuffer indicator test

Plus refactor and cleanup.