export/hazard:

Added `file_ext` parameter (optional) to `_get_result_export_path`.
It defaults to 'xml'.
export/hazard:

Added support for exporting hazard maps as GeoJSON.
export/hazard:

PEP8 cleanup.
export/hazard:

Added a 'nrml' alias for the imported openquake.nrmllib.hazard.writers
and updated references accordingly.
Merge pull request #1228 from larsbutler/geojson-hazmap-export

Hazard map GeoJSON export

[r=matley] [f=1199654]