Convert TimelineDelegate to cpp

There are 2 main reason for doing this:
1. Because I can, I wanted to see if I could do it
2. It gets rid of the janky qml re parenting stuff so should be faster.

src/timeline/HiddenDelegate.qml

@@ -41,6 +41,11 @@ TimelineDelegate {
      */
     required property var author
 
+    width: parent?.width
+    rightPadding: Config.compactLayout && root.ListView.view.width >= Kirigami.Units.gridUnit * 20 ? Kirigami.Units.gridUnit * 2 + Kirigami.Units.largeSpacing : Kirigami.Units.largeSpacing
+
+    alwaysFillWidth: Config.compactLayout
+
     contentItem: QQC2.Control {
         id: contentControl