Hide toplevel from toplevel list when it is being dragged

Uses a custom wrapper widget, that makes `draw` do nothing when visible
is set to false.

This works well sometimes, but can cause weird bugs...

src/widgets/mod.rs

@@ -19,8 +19,8 @@ mod mouse_interaction_wrapper;
 pub use mouse_interaction_wrapper::mouse_interaction_wrapper;
 mod toplevels;
 pub use toplevels::toplevels;
-
-trait Foo {}
+mod visibility_wrapper;
+pub use visibility_wrapper::visibility_wrapper;
 
 pub fn layout_wrapper<'a, Msg, T: Into<cosmic::Element<'a, Msg>>>(
     inner: T,