Support for Approval Tests Java framework

Hi Jon,

I've added a new language/test framework pair, for Approval Tests in Java. This framework produces output in JUnit format which is of course uncomplicated to parse. However, it also produces text files in the sandbox directory, which need to be reported back to the user. So I've added code that scans the sandbox for text files, and adds and removes them as necessary from "visible_files". Then I added an extra call to the existing ajax so that these files would be shown in the GUI. I have added unit tests for this, but nothing that checks the ajax.

If you like this, I might want to add the same approval testing framework for C# and javascript. I intend to use it to teach the principles of approval testing.

Let me know what you think!

Emily