Add Hipchat Support

fixes #3.

This is implemented as a [HipChat addon](https://www.hipchat.com/docs/apiv2/addons). 

No copy-paste configuration is needed, all that is handled by a HipChat webhook. Here's a [live demo](https://pagerbothipchat.herokuapp.com/) of the admin app.

When it's time to deploy, one would set `DEPLOYED` to `true` as usual and then go to "https://hipchat.com/admin/addons" and click on Build and install your own integration. After that, he'd paste the URL of the app in the modal, and the configuration will be done automatically. Hipchat sends in the OAuth ID and Secret to a specified URL, and the app manages the rest. :)

![hipchat](https://cloud.githubusercontent.com/assets/3893573/4841479/1781ddd2-601b-11e4-8656-2dcbe327ac7b.png)







Hmm. I feel bullish about the error handling here since all we're doing is logging - without the escape block, the heroku logs will display the error much better (full traceback, etc) and it would be easier to grep for.