Add the unittestgui test runner, built with Tk, to the Tools directory.

It would be good to have this script included in the bin/ directory of the Mac installer as well.

The unittestgui runner can be found at:

    https://bitbucket.org/markroddy/unittestgui

The code is a modification of the original unittestgui by Steve Purcell and updated for test discovery by Mark Roddy. I have asked Mark if he is willing to help maintain the code and asked him to complete a contributor agreement.