wxWidgets already has a mechanism for locating plugins under
$libdir/wx/*, there's no reason to duplicate it with another
compile-time symbol.
As a consequence, this makes the library relocatable via WXPREFIX again.
Fix the location where the web-extension plugin is installed to be
consistent with the primary bakefile-based build system: i.e. to use
lib/wx/x.y.z for devel versions and lib/wx/x.y for stable.
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.
