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.
@antoviaque In fact. The issue is that the child xblock is proxyed by our adventure xblock. So is the child has a handler named "HELLO", but not the main xblock, it wont work. For this case, it only affects the ooyala publish events since it doesn't need any other callback. But we would have more issues with a mentoring child in example.