Initial implementation of the adventure xblock

Initial implementation of the adventure xblock, build with Backbone + Marionette.

It currently only read the raw xml config.... but this will be modified to use lightchildren. To make this testable on the client side, we can only mock the function that fetch the data in the controller.
Yep, absolutely. Since the "first" name is specified in the main task description, I'll let this as it is now but you are totally right that we could easily get rid out of this.