Update to latest playdoh and freshen up things.

- Updates vendor to the latest playdoh-lib.
- Updates core files (manage.py, playdoh.wsgi, etc.) to match latest
  Playdoh.
- Removes unnecessary migration folders and adds models.py to base
  app.
- Removes unnecessary tests and removes the need for pyquery.
- Removes hmac and hashlib from requirements; they're in the stdlib
  now.
- Removes fixtures and uses factory_boy in tests instead.