B3 template updates

Base bootstrap 3 template now styled to look like it blends right in with 2.3.2 version of CommCare HQ's styles. Fancy footer though. ;-)
This template selection seems a bit verbose, given that it's being done in more than one place. Could the commonalities be refactored into something like `style_utils.get_template(request, "domain_list_dropdown.html")`?

Or maybe this pattern is not expected to stay around for too long, or be done in more places, in which case it's fine.