It's used to sort Votes, takes votes list of 10 items in the API from 5s
to 300ms.

Code by @luxcem, left almost untouched.

remove_dossiers_without_recommendation and
remove_representatives_without_votes are useful to clean the database
before dumping test fixtures.

Also:

- code was PEP8'ed
- tests were added,
- untested code was removed,
- setup.py was fixed and requirements.txt is gone,