Drag and Drop works ok now.

The main functionality works but only in cosmic desktop. So there are
some issues that need to be worked out yet in regards to libcosmic.

src/core/slide.rs

@@ -194,6 +194,12 @@ pub struct Slide {
     video_end_time: f32,
 }
 
+impl From<&Slide> for Value {
+    fn from(value: &Slide) -> Self {
+        Self::List(vec![Self::Symbol(Symbol("slide".into()))])
+    }
+}
+
 impl Slide {
     pub fn background(&self) -> &Background {
         &self.background