Add a lot of tests for many wx GUI classes.
Add tests using the new wxUIActionSimulator class but disable them under OS X
as too many of them currently fail there.
Refactor the test suite to make organizing the existing tests and adding the
new ones easier.
Improve documentation using the information gathered while testing the
classes. Also update the documentation of the testing system itself.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65386 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
