Xblock mods

these are the mods needed to allow the worldmap client to talk to the edX/Xblock adapter.

I don't think any of these will affect the basic running of the embed if accessed via the web directly so it shouldn't have an impact on any existing code and/or uses.

If there is an impact, we can make it so the XBlock adapter has to add a query parameter like:
   .../embed?xblock-adapter

and then all the xblock-specific code would be put into the output stream.