Issue #344: Set default country from selected timezone.

Addresses https://github.com/backdrop/backdrop-issues/issues/344 in setting a default value for the Default Country by looking for parts of the selected timezone in the country list and returning the matching country code.
Good point. I had just copied the country function from above (which is where the sort comes from), but it seems it's used there for sorting the values of the array because they're output in the UI. This list isn't, sort (extra) sorting doesn't make sense here.