Bug 18113 small code improvements

A few more small improvements to add.
http://bugs.mitk.org/show_bug.cgi?id=18113
We disable many MITK modules to speed up our supersuperbuild by simply removing them from `module_dirs` in  `Modules/CMakeLists.txt`. This has worked well for all modules so far except the ToF modules, so I was just looking for a solution. I thought this still worked for the standard case where the ToF modules are enabled, but maybe I'm mistaken or maybe there's a cleaner/more robust solution?