Add bandwidth field to mirror URLs

Not using this anywhere just yet, but suggested by Florian so we can do
some more fancy things down the road, like determine bandwidth by
country.

Signed-off-by: Dan McGee <dan@archlinux.org>
Mirror view tweaks and enhancements

* Add country column to main mirror list overview page. Most mirrors are
  strictly in one country, so do a little magic to show the right
  country if it makes sense.
* Use new way of getting country names so we respect the overrides now
  present in the django_countries package.
* Make the country selection box on the mirrorlist generation page a lot
  taller by default so it is easier to use.

Signed-off-by: Dan McGee <dan@archlinux.org>