Here the biggest changes are in the test application because we
refactor a number of the tests to make better use of the button.
Although applications may consume button events it does have a
default behavior which is to switch to the default application
(usually the clock).
This is a big change that break compatiblity with existing applications
*and* with existing installed versions of main.py.
When upgrading it is import to update main.py:
./tools/wasptool --upload wasp/main.py
