Build System Improvement idea

• We should check the version and required build options of injected external projects. (previously captured in #77)
• Hide CMake variables in non-superbuild dirs: On the superbuild level, we now have only very few, high-level CMake options visible. However, the configured CTK-build directory adds a couple of other non-advanced options which clutters again the list of CMake variables. (previously captured in #107)