[bugfix]: offline QA: ECbmRecoMode::Timeslice as a default for data processing in the CbmQaTask class

In the CbmQaTask the two regimes of input data branches handling are available: loops within CbmEvent objects (ECbmRecoMode::EventByEvent) and loop over entire timeslice (ECbmRecoMode::Timeslice). Previously, the first regime was selected by default, what led to the repeated filling of the histograms in the CA input QA and the CA setup QA. Now this regime should be enabled explicitly in the constructor of the task if the access to the CbmEvent objects and hit/track indices within them is available in the particular QA-task.