Add ability to import spatial data to PostgreSQL/PostGIS

[ethanwhite]

PostgreSQL with the PostGIS extension allows spatial data to be stored in a way that allows spatially explicit querying. It would be nice to support this in two ways:

1. Allow importing of strictly spatial files (rasters, shapefiles, etc.). These kinds of files could only be imported into PostgreSQL.
2. Allow importing tabular data that has a spatially explicit component (e.g., site locations with latitudes and longitudes) as a spatially enabled table.

The later should be optional and both approaches would need to be constrained to PostgreSQL and any other formats (HDF5?) that support spatially explicit data.

[ethanwhite]

Also SQLite using http://www.gaia-gis.it/gaia-sins/

[jainamritanshu]

@ethanwhite @henrykironde I would like to work on this.

[ethanwhite]

Implemented in 7d84795.