Show contributors even if GH is disabled

:convenience_store: 

This shows the top "Contributors" link even when GH is disabled, so you can look at the existing contributors.  I also hid the "Your Agreements" section on that page, because it is full of links that take you to pages for becoming a contributor and signing a CLA.

![](https://dl.dropboxusercontent.com/s/9yqsqim3nz1km0s/2014-12-16%20at%204.18%20PM.png?dl=0)

Closes https://github.com/opscode/supermarket/issues/909