Add HipChat notifications (keeping the same config notation as start-not...

Adding options to HipChat so it can be configured to report on different events (particularly BackToNormal and Failure whilst turning off Success to make Jenkins less noisy in a room). Made it fairly noisy by default and kept the same semantics as 'start-notify'. So a config to only report on error and returning to green build would be:

```
hipchat:
        room: '{{hipchat_room}}'
        start-notify: false
        success-notify: false
        aborted-notify: false
        unstable-notify: false
```

(I can flip the true/false default values the other way too if specifying what *does* get reported seems cleaner)