Header/Footer/Nav of new site Bug#913669

Removed old site assets, created new header and footer files independent of old global submodule, added new css, js, and img assets.
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.