Fix row overlap in OutlineView

TreeViewDelegate doesn't auto-size from contentItem. Explicitly bind
implicitHeight to contentColumn.implicitHeight so rows size correctly.

ui/qml/OutlineView.qml

@@ -50,6 +50,7 @@ TreeView {
         readonly property int bodyIndent: 12
 
         implicitWidth: tree.width
+        implicitHeight: contentColumn.implicitHeight
 
         background: Rectangle {
             color: del.current ? theme.highlightColor : "transparent"
@@ -58,6 +59,7 @@ TreeView {
         }
 
         contentItem: ColumnLayout {
+            id: contentColumn
             spacing: 4
 
             RowLayout {