make i18nTestCase a pure mixin class
make test for checking if we have js catalog files available
move uninstalling of a language to i18nTestCase too
call collectstatic once we finish creating the js catalog files for a language
simplify the js catalog test
place js catalog files onto the toplevel static dir
place js catalog files into i18n/static dir
Merge pull request #2032 from aronasorman/properly_place_js_catalog_files

Properly place js catalog files