Push to card specs and scenarios

These are the specifications and scenarios for push to card.

Scenarios still required:
- [x] Credit to a card with `can_credit` of `false` should fail

Open issues required to merge:
- [x] Card.type and Card.category defaults #607 
- [x] Use `bank_name` instead of `bank` #608 
- [ ] Exceeding transaction limit should product a 409 instead of 400 #611