Lightweight preview

[pdpinch]

As a curator and course author, I appreciate being able to preview learning objects in situ with their full course context, but that can be slow and sometimes I just want to see the learning object by itself. I'd like to have an option for a lightweight preview that doesn't involve opening a new window/tab. It doesn't even have to be interactive, although that would be nice.

I can think of two options for this:

1. We can look use the course block api to render and return a single block. However, authentication may still be slow.
2. @amir-qayyum-khan spent some time earlier developing a tool for creating screenshots of xblocks that we could start working on again. We stopped working on this when we developed the current preview method of linking out to an instance of edX.
3. @giocalitri suggested creating an app based on xmodule and passing the XML to it