More translation updates

* Django settings to tell Django what languages we're using and where
  to find our translation files.
* Mark more strings for translation.
* Update the comments at the top of locale/fr/LC_MESSAGES/django.po
* Add some doc for how to translate
* Fix use of blocktrans in some templates
* Update finaid doc while I'm here
* Ran make_messages & compile_messages to update the translation files.