geonode2-integration geoserver data management refactoring

Refactored geoserver data population from a rest-api-style approach to a dump/restore content approach.

A new bash script (openquakeplatform/openquakeplatform/bin/oq-gs-builder.sh) allows to dump to filesystem, drop or restore from filesystem an entire geoserver dataset.

**NOTE:** it introduces a new dependency on xmlstarlet utility.