Prepopulate StudyArea table

[beamalsky]

I'm working on a StudyArea creation view (see #124) that lets users draw arbitrary geometries. However, I suspect UCD has some geometries they'd like to preload for common study areas: eg: Philadelphia, West Philly (/Philly neighborhoods), Clark Park, the Porch. I think we should ask them about this and see if they can share GeoJSON files that we can preload for them.

[beamalsky]

As we enter the final stretch of this project, it's become clear that we need a model for saving custom geographies for ACS data to compare to collected survey data. Instead of having three distinct location models (StudyArea, Location, and ACSArea), I wonder if it makes sense to combine StudyAreas and ACSArea somehow. Let's discuss!