bin/openquake:

Added '--export-type' command line option.

Options are 'xml' and 'geojson'.
bin/openquake:

Cleaned up documentation for `Export` command line options.
bin/openquake:

"store", don't "append" the --export-type parameter.
bin/openquake:

Pipe the --export-type parameter to the export functions.
export/risk:

Added loss_map geojson export support.
Merge pull request #1227 from larsbutler/geojson-lossmap-export

GeoJSON loss map support

[r=matley] [f=1198843]