SAFE_TARGET_FPS property is not support in CMAKE configurations

When using Qmake it was possible to set the target FPS rate using SAFE_TARGET_FPS property in the qmake files. In CMake configurations, that property is missing.

That should be added to the QSR Cmake configuration and also document in the user manual.

As a workaround, it is possible to set the SAFELAYOUTTOOL_TARGET_FPS environment variable when building QSR application.