Balanced

Lots of stuff going on here:
* [x] Remove braintree JS in favor of balanced JS
* [x] Add a profile for users and store card and bank tokens from balanced in it 
* [x] Refactor some DRF code and add django-rest-swagger for API docs at `/docs/`
* [x] Create a special APIView and template for retrieving a user's bid via `/bid/?url=`