[WIP] Accept Github webhooks payload

This is the first step in implementing #5. Add a webhook to your repository with a URL in the following format:

```
http://<your-ip>:6161/webhooks/receive/<project-id>
```

... and DCIY will automatically build branches when they're pushed. Pretty neat! It's starting to feel like a proper CI, now.

This is the very core functionality for that ticket, though; it's pretty unrefined. What's left to do:

- [ ] Show new builds live as they happen, with some kind of CoffeeScript polling on `projects/:id/builds`.
- [ ] Either add a button to register the hook with the GitHub instance, or show you a "help" page that walks you through how to do it.
- [ ] Build incoming pull requests, too! Maybe. This has Security Implications :tm: like @cobyism brought up earlier.