DetectorHistogrammer: Evaluate Efficiency

This MR enables the DH module to also evaluate the efficiency of the detector. The most notable change required for this is the removal of the MsgFlag::REQUIRED from the PixelHit message. In turn, before using it we have to check for a nullptr.

In addition, the Cluster class has been cleaned up a bit (changed names of members to remove redundancy, made a few const) and the logging verbosity has been adapted and some plotting ranges have been corrected.