WIP:  getting slides from git

This isn't working -- it's the git part of the puzzle, though. 

This is change to the Class object to get the slide names from Git. Except since node is all async, it's happening asynchronously.  I'm sure there's some Node trick or idiom here; this virtual method is expecting something synchronous. I don't think I'll figure out all the ins and outs of how Node expects people to work with the exec library at 5 AM. The git part of the problem is working.