Battles Resource

Hiya!

The goal of this section is to introduce a second resource so we can start linking. In fact, we show a *really* simple link, and make it better in the next section. Steps:

- Feature/Scenario for creating a new battle
- create the basic POST endpoint
- add validation
- GET scenario and controller code
- link Battle to Programmer with a VirtualProperty

As always, ignore those silly commits :).

Thanks!