Exercise Level Navigation

This provides a side bar navigation to view exercises. This should be a pretty big help for managing the page loads.

It looks like we're holding steady with the number of submissions on that ruby page. @kytrinyx, you may want to pull this down and take a look before merging in. It's functional but a fairly major UI change. Our active submissions don't seem to have that explosive growth anymore so this is probably slightly less of an emergency.