Use a custom progress bar UI on mac to see the green / red status colours

Seeing the progress bars green on success and red on failure is an big part of the test-driven experience.  

On Aqua Look&Feel (mac), the progress bar widget ignores changes to foreground color, thus the progress bars are always on the color of the selected theme (blueish or greyish) regardless of the fail/success status.

This pull request use a custom class for the progress UI that accepts the foreground color changes enabling green and red visual statuses.