oq-ui-api/geonode/exposure/views.py:

Factored out the csv/nrml generator code into separate helper functions
to increase readability.
oq-ui-api/geonode/exposure/util.py:

Removed unused function.
oq-ui-api/geonode/exposure/forms.py:

Added some more detailed documentation to the BuildingExposureForm
to explain the dynamic choice of admin levels.