Refactor to use a get_remote() command so that it can be easier to retrieve the matching URL.

Want to be able to expose an option to push to the remote branch but hard to do so without knowing the remote URL.
Expose a githubconfig prompt-to-push option to allow prompting to push to GitHub in the event that the branches are not located there.

Dependent on changes made in: https://github.com/seveas/git-hub/pull/13

More fixes.