add a little color to hipchat pass/fail messages

Color matters - :green_apple: :red_car: 

I've added two configuration options to `properties` of hipchat-notify, `passed-color` and `failed-color`. You can set them in the `after-steps` of your app's wercker.yml, just like `token`, `room-id`, etc. The defaults for `passed-color` and `failed-color` are "green" and "red" respectively.

Enjoy!