Remove / reattach '-' prefix from fields given to ``order_by`` for rewriting to work.
Added a simple test that catches the descending order problem.
Flake8, remove unused variables.
Merge pull request #133 from wrwrwr/feature/descending-order-with-translation-fix

Fix ``order_by`` on descending translation field
Update AUTHORS file.
Fix descending order rewriting in all ordering calls.