Move panel into an old-panel subdirectory

We expect to replace this with applets running under
https://github.com/pop-os/cosmic-dock-epoch.

src/popover_container.rs

@@ -1,89 +0,0 @@
-use cascade::cascade;
-use gtk4::{glib, prelude::*, subclass::prelude::*};
-
-use crate::deref_cell::DerefCell;
-
-/// Unlike gtk4's `MenuButton`, this supports a custom child.
-#[derive(Default)]
-pub struct PopoverContainerInner {
-    child: DerefCell<gtk4::Widget>,
-    popover: DerefCell<gtk4::Popover>,
-}
-
-#[glib::object_subclass]
-impl ObjectSubclass for PopoverContainerInner {
-    const NAME: &'static str = "S76PopoverContainer";
-    type ParentType = gtk4::Widget;
-    type Type = PopoverContainer;
-}
-
-impl ObjectImpl for PopoverContainerInner {
-    fn constructed(&self, obj: &PopoverContainer) {
-        let popover = cascade! {
-            gtk4::Popover::new();
-            ..set_parent(obj);
-        };
-
-        self.popover.set(popover);
-    }
-
-    fn dispose(&self, _obj: &PopoverContainer) {
-        self.child.unparent();
-        self.popover.unparent();
-    }
-}
-
-impl WidgetImpl for PopoverContainerInner {
-    fn measure(
-        &self,
-        _obj: &PopoverContainer,
-        orientation: gtk4::Orientation,
-        for_size: i32,
-    ) -> (i32, i32, i32, i32) {
-        self.child.measure(orientation, for_size)
-    }
-
-    fn size_allocate(&self, _obj: &PopoverContainer, width: i32, height: i32, baseline: i32) {
-        self.child
-            .size_allocate(&gtk4::Allocation::new(0, 0, width, height), baseline);
-        self.popover.present();
-    }
-
-    fn focus(&self, _obj: &PopoverContainer, direction: gtk4::DirectionType) -> bool {
-        if self.popover.is_visible() {
-            self.popover.child_focus(direction)
-        } else {
-            self.child.child_focus(direction)
-        }
-    }
-}
-
-glib::wrapper! {
-    pub struct PopoverContainer(ObjectSubclass<PopoverContainerInner>)
-        @extends gtk4::Widget;
-}
-
-impl PopoverContainer {
-    pub fn new<T: IsA<gtk4::Widget>>(child: &T) -> Self {
-        let obj = glib::Object::new::<Self>(&[]).unwrap();
-        child.set_parent(&obj);
-        obj.inner().child.set(child.clone().upcast());
-        obj
-    }
-
-    fn inner(&self) -> &PopoverContainerInner {
-        PopoverContainerInner::from_instance(self)
-    }
-
-    pub fn popover(&self) -> &gtk4::Popover {
-        &self.inner().popover
-    }
-
-    pub fn popup(&self) {
-        self.popover().popup();
-    }
-
-    pub fn popdown(&self) {
-        self.popover().popdown();
-    }
-}