Payment signals BOOK-741

- setup the status mappings for order, order_payments and payments
- added FSM for three components
- created signals for the three components
- added some basic tests
- updated migrations to remove references to abstract classes
- added start of guard file for watching tests
The Gemfile is a ruby thing for installing dependencies and the guardfile is for using guard to watch for file changes and then run the python tests. I couldn't find a decent python alternative for doing this.