exposure export tool: add support for downloading population and dwelling fractions separately

[Ben Wyss]

In the exposure export tool the user need to be able to make a selection of what data should be included in the download:
    1) full download (the data that is currently downloaded by the tool
    2) only the population for the selected area
    3) only the dwelling fractions for the selected area

Option 2 and 3 can only be available in csv.

[Lars Butler (lars-butler)]

Pull request: https://github.com/gem/oq-platform/pull/38

[Lars Butler (lars-butler)]

Fix for incorrect ToD handling implementation: https://github.com/gem/oq-platform/pull/41

[Paul Henshaw (paul-sl-henshaw)]

Following a discussion with Chiara it seems that we have a need to obtain dwelling fractions for a number of points (selected by name or specified by the user (see https://bugs.launchpad.net/oq-platform/+bug/1221816) ) without calculating a population fraction value .

Essentially the export tool would continue to operate as it currently does but instead of outputting the calculated population value, the following columns should be output for each cell:

 total_population (in cell)
 is_urban
 building_type
 dwelling_fraction

Where available we would also like to obtain the following values from the distribution_value table:

 avg_dwelling_per_build
        building_fraction
        avg_floor_area
 replace_cost_per_area

and the following values from the study_region_facts table

 avg_peop_dwelling,
        avg_dwelling_area

I think it makes sense to output this kind of data in CSV format only since further processing is required before it can be used with the oq-engine.

[Paul Henshaw (paul-sl-henshaw)]

See also https://bugs.launchpad.net/oq-platform/+bug/1221814 for "Add support for exposure export by named region"

[Paul Henshaw (paul-sl-henshaw)]

Updated status - there is still work to do.