Windows key generates Mod4+Super (at least with the version of Gdk we use on
linux) so for bindings using the Windows key to work, GDK_SUPER_MASK has to be
added to modifier mask.
guint Keyboard::PrimaryModifier = GDK_CONTROL_MASK; // Control
guint Keyboard::SecondaryModifier = GDK_MOD1_MASK; // Alt/Option
guint Keyboard::TertiaryModifier = GDK_SHIFT_MASK; // Shift
-guint Keyboard::Level4Modifier = GDK_MOD4_MASK; // Mod4/Windows
+guint Keyboard::Level4Modifier = GDK_MOD4_MASK|GDK_SUPER_MASK; // Mod4/Windows
guint Keyboard::CopyModifier = GDK_CONTROL_MASK;
guint Keyboard::RangeSelectModifier = GDK_SHIFT_MASK;
guint Keyboard::button2_modifiers = 0; /* not used */