Resolves #323, along with a few other minor improvements to Gist support.
* Makes treelist.html slightly more general to support showing gists as well (removes gistlist.html)
* Adds proper github links to non notebook gist files
* Remove trailing table row for next-prev buttons if there aren't any to show
* Columnizes the user gist view page
Merge pull request #325 from icook/master

Resolves #323, along with a few other minor improvements to Gist support...