Make Print key behave like a super key

Print key is designed to take screenshots.

A super key is named `Mod4` for X11 and i3wm.

Install/Templates/system/X11/xkb/symbols/pc

@@ -36,7 +36,7 @@ xkb_symbols "pc105" {
     modifier_map Lock   { Caps_Lock };
     modifier_map Control{ Control_L, Control_R };
     modifier_map Mod2   { Num_Lock };
-    modifier_map Mod4   { Super_L, Super_R };
+    modifier_map Mod4   { Super_L, Super_R, Print };
 
     // Fake keys for virtual<->real modifiers mapping:
     key <LVL3> {	[ ISO_Level3_Shift	]	};