Bulk app translations

Addresses: http://manage.dimagi.com/default.asp?130884

I considered moving much of the translation logic added in `corehq/apps/app_manager/views.py` to the `Form` or `XForm` classes. Any thoughts on that?
I thought it did that at first too. Turns out it just updates the xml of the given Form with the given xform xml. It doesn't persist the Form object though.