Custom Toplevels widget

Fixes centering on toplevels.

Need to use fewer hacks, and add equal scale factor.

See if Iced layout system can be improved.

src/widgets/workspace_item.rs

@@ -1,5 +1,7 @@
 // TODO rename
 // combine widgets
+// Hack: this widget defines it's width as the second child's width
+// So the width of the image will be the overall width.
 
 use cosmic::iced::{
     advanced::{
@@ -62,7 +64,10 @@ pub struct WorkspaceItem<'a, Msg> {
 
 impl<'a, Msg> Widget<Msg, cosmic::Renderer> for WorkspaceItem<'a, Msg> {
     fn width(&self) -> Length {
-        Length::Fill
+        //Length::Fill
+        // XXX doesn't work when used in standard `row` widget
+        // But fixes allocation of `dnd_source` wrapping this, within `Workspaces` row
+        Length::Shrink
     }
 
     fn height(&self) -> Length {