Make it easy to geocode cities for the map

1. The new process: Add each city to the `data/locations.yml` file.
2. Run `rake locations`. This will generate an appropriate
`public/data/locations.json` file
Add locations from Google Spreadsheet
Update with the feedback from @coreyhaines
Merge branch 'maintainable_locations' of https://github.com/graysonwright/GDCR into graysonwright-maintainable_locations

Conflicts:
	Gemfile
	Gemfile.lock