COMP: Build SlicerBaseCLI only if VTK is found.

This CMakeLists can be configured by projects others than Slicer
(e.g. TubeTK) that may not have VTK.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22122 3bd1e089-480b-0410-8dfb-8563597acbee