- Make transitions between pages always be contiguous
  the children list order affects the paint order - so you can use set_child_above_sibling/set_child_below_sibling
- Add a scroll direction to the animation
  (back to parent to the left, to a child to the right)
- see about theming again, seems that some panels have the wrong colour
- warning when panel startup takes too long? no animation for the date & time for example
- implement vertical orientation