Fix for the Hide games checkbox...

Adjusted text color of Hide Games checkbox to be legible in both white and dark themes.  I couldn't figure out how in WPF to make the background of the checkbox LABEL appear with a dark background, it just sets it transparent.  I just made this a medium grey which looks fine between the dark and light.

I can look at changing this to a toggle button instead of a checkbox, which would then have its own background, but wanted to get this hotfix in first.