This change provides some functionality for listing all accessible

repositories on GitHub owned by the authenticated user, another user, or

an organization. This will eventually be used for the new repository

configuration UI.
This is based on Olessia's work as part of UCOSP in late 2013/early

2014. It updates her work for the GitHubClient changes recently made,

abstracts out API list pagination support, and fills in some of the

documentation.

Unit tests pass.
Tested by hand on the command line with my user, David's user, and an organization.