1) Only output to CMAKE_XXX_OUTPUT_DIRECTORY without
worrying about CMAKE_CONFIGURATION_TYPES

2) Use CMAKE_CFG_INTDIR to correctly set CMAKE_LIBRARY_PATH
after the change 1)

3) Use mark_as_superbuild() to pass variables to external
projects and innerbuild. (${PROJECT_NAME}_EP_ARGS)

4) Remove unecessary steps in eigen project (only includes, no lib)

5) Use standard imstkAddExternalProject for Uncrustify (not tested)