if it is running under single_top.cpp or under a project manager.
*) Test Kiface().IsSingle() when adding menus, some operations are not permitted
when running under a project manager and the KIWAY_PLAYER is pegged to a
specific project.
*) Implemented KIWAY::KiFACE() so it loads *.kiface files. They still have to be
in the same directory as the main *.exe launcher, so this presents some difficulty
when the binaries are not yet installed but rather the *.kiface files are still
in their original build directories. For today, I simply copied _pcbnew.kiface
to build/kicad/.
*) Add a test case to kicad/mainframe.cpp just to get an early peek at loading
_pcbnew.kiface under the C++ project manager. Got that working for one
specific invocation just for proof of concept. Surprise, it works.