Adding RailsBridge Boston 1.2014 ruby workshop mods

Modifications include:
* fleshing out all the sites/ruby workshop content -- janetriley, mxie, dpickett
* Adding the 'challenge' tag to the dsl -- dpickett
Fix issues with Ruby curriculum updates

* Goals that had markdown blocks now actually show up
* Fix "next_step" and "back to" to work with pages that have colons
* Prune some empty-ish pages
* Remove 'objects.step' (dupe of classes.step)