Country and City fields in auth_userprofile

ECOM-128 adds a country dropdown to student registration (implementation expected soon). Leveraged a field added months ago but never documented, uncovered the city field as well.
@wedaly please verify and be sure to let me know when this goes live. 
@gabe or @brianhw , FYI & sanity check please.
@srpearce please proof read/copy edit.