Make buttons blue on keyboard navigation

- Make buttons blue when they have activeFocus to make it more
  clear which button has focus when using keyboard navation.
- By default most components only respond to 'space' on keyboard
  for pressing buttons and toggling checkboxes.
  Map Enter/Return (normal and keypad) as well.

qmlcomponents/ImCheckBox.qml

@@ -0,0 +1,14 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright (C) 2022 Raspberry Pi Ltd
+ */
+
+import QtQuick 2.9
+import QtQuick.Controls 2.2
+import QtQuick.Layouts 1.0
+import QtQuick.Controls.Material 2.2
+
+CheckBox {
+    Keys.onEnterPressed: toggle()
+    Keys.onReturnPressed: toggle()
+}