[GTK3] Ruler: replace pixmap with pixbuf and use double-buffering
Submitted by b'Matas Brazdeikis'
Assigned to b'Matas Brazdeikis'
It was started code for double buffering of pixmap. It was incompleate. Reworked it.
Uses cairo.Surface and pixbuf to replace pixmap, as it is deprecated in GTK3.
Imported from https://bugzilla.gnome.org/show_bug.cgi?id=675238