_Quickfix_ to enable inversion of colors in the Image Viewer. This is

important as it enhances contrast, making it easy to view the galaxies
under low-light conditions.

This should be redone in a more elegant way, adding more options, but
this is a quick feature for now. If there are any objections, do feel
free to revert / discuss them.

I almost did this because I needed it right away.

CCMAIL: kstars-devel@kde.org