add compatibility with gnome 42 and a minor bug fix

[massimiliano-dalcero]

add compatibility with gnome 42 and a ug fix Also, I add a delay time during sliding, for avoid flickering when switch desktop using shortcut

[massimiliano-dalcero]

I made some of the required changes

I kept the variable instead of the constant, because I think it can't be done differently with the new gnome color system

i kept the callback without using arrow syntax. I changed the function name to _changeWallpaper_delay instead of _changeWallpaper2

I need to do something inside this "Pull request"?