Merge master with dorothea
work on cmake:
- compile sub-projects as libraries, link to main executable
- use target_include_directories to make include directories known to each sub-project
added checker directory containing the essential parts of the efficiency calculator by Manuel Schiller, still need to give proper input from cuda/velo output
why does code in x86/velo/clustering depend on the cuda code in cuda/velo/mask_clustering? Intuitively, that should not be the case (?)