ix the problem with the original template-based implementation to limit
the amount of things that could be forgotten by new panel creators
(since we can't just have a static fail method warning about things
beinf forgotten).
This reverts commit a92516bcd2.
On wxWidgets 3.0, SetSizeHints must be called once the panel is fully populated.
On wxWidgets 3.1.5, SetSizeHints is not mandatory but can be called to ensure
right sizes once the panel is fully populated.