Issue #200: libpng error popup (dismine/valentina)

New issue 200: libpng error popup https://bitbucket.org/valentinateam/valentina/issue/200/libpng-error-popup

Peter Gsellmann:

Everytime the main window or the Preferences window opens, there are error popups from the PNG-library saying

“libpng warning: iCCP: known incorrect sRGB profile”

This is with libpng version 1.6.6

The problem and solution is described in https://wiki.archlinux.org/index.php/Libpng_errors

All PNG-files should be stripped as described on this page