Xfce4 fix wallpaper setting

[codedwrench]

This pull requests makes it so that OneShot can set wallpapers and colors properly again on the newest xfce version.

Xfce no longer listens to monitor0 when setting a wallpaper and instead needs the display name, e.g. backdrop/screen0/monitorHDMI1/workspace0/last-image

Colors also didn't seem to work properly, so that has been changed to use rgba1 values, also using xfconf_channel_set_array instead, to make things easier

It sets the wallpaper to all monitors. Resetting when closing the game also works.
Tested through modshot, because i wasn't able to compile using conan, however this file is nearly the same in either fork

[codedwrench]

After a lot of messing about with the cmakelists i was able to replace the modules missing in conan with my own and it seems gtk3 is required for the new features. I think I could use the GDKScreen apis instead: https://docs.gtk.org/gdk3/class.Screen.html but most linux systems nowadays should have gtk3

[codedwrench]

took a while, but here it is using your fork as well