Updated to REQUIRED for ITK, and CMake version.
Updated to REQUIRED for ITK, and CMake version.

With the REQUIRED flag, there is no longer need for checking on whether
ITK has been found or not.  Also, the required version of CMake is now
made explicit.

InsightSoftwareConsortium/ITKTutorialExercises,InsightSoftwareConsortium/ITKTutorialExercises