location of libexec files can't be tuned in app-framework

The location of the framework binding can not be tuned but is fixed to be ${CMAKE_INSTALL_FULL_LIBEXECDIR}/${afm_name}

This default location is good but it is important to be able to tune that location. This at least has the good effect that the location is set at one point in the build system instead of at multiple point as today.

The same issue exists in app-framework-binder.