Create a derived class and add it to wxUiTesting

Description:

We need to create a control that is derived from a standard wxWidget's control so that we can add it to our test app to test the derived_class property. Ideally, this would be something other people might want to use.

Most of the widgets I've found on github use a GNU license, so you can't use them in any project like ours because it requires changing the entire repository's license. Even repositories that already have a GNU license cannot legally use a widget that has a GNU license with a different version since the GNU license specifically disallows using two different license versions.