(WIP) 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.
This is more debug than info, and could include actual values (block id, step name, etc.) -- similar comment for a lot of these throughout the PR