[email protected]: Make mult-instance capable. (#13678)

InhibitController will now inhibit/uninhibit, keep track of
cinnamon's own handle and the list of currently inhibiting apps.

This allows the applet itself to be simplified and become multi-
instance capable.

Author: mtwebster

data/theme/cinnamon-sass/widgets/_menus.scss

@@ -52,6 +52,10 @@ $menuitem_border_radius: $base_border_radius * 1;
   icon-size: $scalable_icon_size;
 }
 
+.popup-inhibitor-menu-item .popup-menu-icon {
+  icon-size: to_em(24px);
+}
+
 // popup submenus
 .popup-sub-menu {
   border-radius: $base_border_radius + 1;