Show tooltip with full playlist item text on hover

Some titles might be more than few words and will not fit in current playlist popover. Instead of stretching it, show full playlist item filename (or path) on hover in a tooltip.

src/playlist.js

@@ -119,6 +119,7 @@ class ClapperPlaylistItem extends Gtk.ListBoxRow
             this.isLocalFile = true;
         }
         this.filename = filename || uri;
+        this.set_tooltip_text(this.filename);
 
         const box = new Gtk.Box({
             orientation: Gtk.Orientation.HORIZONTAL,