resolves numenta/nupic.wallboard#13 Added github labels to PR report.

Addresses the need for Github labels to be shown on the PR report. Some things to note:

* Requires a new node module - github
* Added github credentials to the config yaml files. Valid credentials will need to be put in there for production.
* The server now makes a call to Github for information on each PR in the array in order to get the label data. It would be nice to make only one call, but I could not find a Github API call that would do that.
* On github, the text within the labels are sometimes white, sometimes black, which helps with legibility. On the wallboard, the text is always white, which can make it hard to read on some labels which have a light background color. This could be addressed if we used Less CSS to calculate the lightness of the background color and adjusted the text color accordingly.