Workflow content update

Updates the workflow response to be the same as what brian posted in #212. Adds versioning to the workflow model and so closes #206.
I think I've almost exclusively written string interning using that form in lieu of `.to_sym` 

eg
+ https://github.com/zooniverse/Panoptes/blob/72f05335484253589e36a85525f58a9c4a730377/lib/role_control/enrolled.rb#L15
+ https://github.com/zooniverse/Panoptes/blob/076fc442455c980c4ee91122cb96b42ed342e4a5/lib/role_control/roled_controller.rb#L7