fixed lots of bugs by return Action enums in song_editor and library

Instead of dealing with a complication of every return from a
component being a Task<Message>, I create an Action enum that only
contains Tasks when needed and other specific actions that the
overarching App should handle to interact with other parts of it.

src/ui/mod.rs

@@ -1,3 +1,5 @@
+use crate::core::model::LibraryKind;
+
 pub mod double_ended_slider;
 pub mod library;
 pub mod presenter;
@@ -11,3 +13,14 @@ pub enum EditorMode {
     Presentation,
     Slide,
 }
+
+impl From<LibraryKind> for EditorMode {
+    fn from(value: LibraryKind) -> Self {
+        match value {
+            LibraryKind::Song => Self::Song,
+            LibraryKind::Video => Self::Video,
+            LibraryKind::Image => Self::Image,
+            LibraryKind::Presentation => Self::Presentation,
+        }
+    }
+}