Replace BAO-level country default for proximity searches with a client-side default

Angular architecture problems made it difficult to set a default value for the country on the client side, so I did so on the server side in this band-aid pull request.

Also worth noting is that the choice of the default country is based on the localization setting for "Default Country" under Contact Address Fields, which is described as the "value ... selected by default when adding a new contact address." Using this to specify default search parameters might be a bit of an appropriation.