bin/geocode script for testing geocoding

Run bin/geocode -h for options.

Has:

 * configurable cobrand / config-file / geocoder
 * some diagnostics for missing cobrand

Minor fixes rebased into this commit:

 * bin/geocode error if no --cobrand passed
 * bin/geocode docs and accept GEOCODER as string

Notable TODOs remaining:

 * reverse geocoding, to double check that latitude actually maps
   somewhere useful (and is within Cobrand's boundaries)
 * diagnosis of relevant CONFIG settings
 * flag to disable caching