Simple QA of DigiEvents implemented in algo, with offline integration into cbmreco_fairrun.

The previously existing QA for digi events (histogramming the digi time within the event) was implemented in reco/tasks/CbmTaskDigiEventQa and integrated in the "offline" binary cbmreco_fairrun.

In order to integrate it into the online process cbmreco, the algorithm was re-implemented in a ROOT-free fashion in algo/qa/DigiEventQa. An auxiliary, ROOT-free and lightweight histogram class Histo1D was implemented along.

The algorithm is integrated into CbmTaskDigiEventQa, replacing the native implementation there. The resulting CBM histograms are translated to ROOT TH1Ds, which are communicated to the histogram server. How the communication to the latter from algo/cbmreco without binding to ROOT can be accomplished remains to be seen.

In the process of re-implementation, the QA was extended from STS to all detectors in the setup.

N.b.: The histogram class can surely be further optimised. I did not invest too much scrutiny here, since I first would like to see whether it is considered of use at all.