(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.
@dragonfi Good point - for shared library resources unit tests are important, agreed.

And good to know for the task of moving utils to the library - this is currently planned for next week as part 3 of the implementation, and could be split out to allow you to take it. I'm noting to ping you on the task when it is split and available for the taking, if you manage to complete the unit tests this week we can include it in your sprint next week.