Adds (tested) Graph and Edge classes

This has the Graph and Edge classes.  As far as I know everything's working, but it's possible I added extra quotation marks to the digraph output, and I can't test that on this computer.

There's some commented out code in Graph.java that uses a Vertex class.  I originally wrote and used one of those, but it was basically just a wrapper for the filename, so I just made Graph use the names instead.  I can upload the Vertex.java if it becomes necessary though.

Did a second commit;  WebPages now adds new pages to the graph and extracts links from them, too.  Or it ought to--I haven't tested it yet.  I didn't do the section under "Augmenting Retrieval" in the propmt, because I couldn't figure out where exactly you were computing cosine similarity and using it to sort/rank pages in your code.  I also haven't set it up to handle the new input format.  So that and testing are the projects for tomorrow, I guess.