Mayavi 4.7.4 ships with a bad png file

The png file mayavi/core/ui/images/preferences.png has the same problem that was reported here in 2018, resulting in a
"libpng warning: iCCP: known incorrect sRGB profile" print out when using Mayavi.
This can be fixed in many ways (see https://stackoverflow.com/questions/22745076/libpng-warning-iccp-known-incorrect-srgb-profile). I used pngcrush.

This is a but a minor annoyance. But getting sidetracked like that while debugging several crashing bugs and severe visualization problems, is not fun...