Adding new model for localized version of the agreement.
Add migration for new model.
Configure inline for translated versions of the agreement.
Add unique constraint and recreate migration. Add helper for getting the localized version of a PDF.
Adjust the agreement view/template to render the correct version per the user's language.
Break out the custom upload_to functions to make them more clear.
Fix typo and shorten upload_to function names.
Merge pull request #171 from mozilla/158-localize-agreements

Localize Agreements