Fix wrong library name in wx_add_sample() for webrequest.
Also prefer to disable wxWebRequest if no backends for it are available,
for consistency with the other libraries.
Rename all library targets to start with wx. This way it does not use generic
names like base or core that could interfere with other libraries that add
include the wxWidgets project.
Add CMake build system for libraries, tests and samples
update_files.py converts build/files into CMake format.
build/update-setup-h has been modified to update build/cmake/setup.h.in.
