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?
This seems like fixing a symptom of a bug rather than the real bug. Looks like somewhere a Python `None` value is being converted directly to a string and it should be converted to an empty string. Is that true? Is https://github.com/dimagi/commcare-hq/commit/55f98104e7febb9d1be70a61edd630de13138cda related?

Seems like a translation that is intentionally set to "None" will be converted to an empty string. That might be unlikely, but would be confusing/frustrating if it ever happened.