Added Errbit integration

![](http://i.imgur.com/LuPs7z6.png)

Hi there, I've added an [Errbit](https://github.com/errbit/errbit) integration, using a new `ExceptionTracker` widget. This widget shows the number of unresolved errors, as well as when the last error occurred.

Errbit is an open source clone of [Airbrake.io](https://airbrake.io/pages/home), so it should be easy to also write an `Airbrake` widget that uses `ExceptionTracker`.

I would also love to see Graph support in the future, to show how many errors have occurred over the last 24 hours, etc. How should I go about adding a datapoint for Errbit? Would you recommend configuring the URL and API key in environment variables, like Graphite?

Oh, and please let me know if I should have submitted this PR to https://github.com/fdietz/team_dashboard_plugins, instead.

Thanks!