Make back button bigger as it is hard to tap with your thumb

resources/qml/TopBar.qml

@@ -35,6 +35,8 @@ Rectangle {
             Layout.row: 0
             Layout.rowSpan: 2
             Layout.alignment: Qt.AlignVCenter
+            width: avatarSize
+            height: avatarSize
             visible: TimelineManager.isNarrowView
             image: ":/icons/icons/ui/angle-pointing-to-left.png"
             ToolTip.visible: hovered