Decode geolocation data from GeoIP cookie, if present

* Remove 'Geo' global configuration variable. It was never a configuration
  variable, but rather a way of injecting a blank object into global scope so
  property lookups on window.Geo don't throw ReferenceErrors.
* Instead, if window.Geo is unset at the top of bannerController.js, attempt to
  parse geolocation data from GeoIP cookie.
* If the cookie is not present, a blank GeoIP object is created.
* While we're waiting for the cookie to roll out to production, the
  <script src="//bits.wikimedia.org/geoiplookup"></script> tag will continue to
  override the blank object with actual GeoIP data.
* Once the GeoIP is rolled out to production, we'll remove the <script> tag.
* The GeoIP cookie is currently being set on the beta cluster.

Change-Id: I1a08c81da7a6ad7e92ab501d4e2ee908fed7be38
Merge "Decode geolocation data from GeoIP cookie, if present"