Main Updates:

Main Updates:

- AliAnalysisMultPbCentralitySelector: when running on data, uses
  AliESDcentrality by default, when running on MC a cut on the
  selected tracks

- AliAnalysisMultPbTrackHistoManager&AliAnalysisTaskMultPbTracks.cxx:
  added histograms for particle species, multiplicity histogram,
  changed pt binning (same as 900 GeV pp now)

- AliAnalysisTaskTriggerStudy: added venn-like histo

- AddTaskMultPbPbTracks.C: forgot in the initial commit

- run.C&run.sh: changes to run on grid (not yet working), loading
  extra classes through a TList, possibility to give a custom prefix
  to the output folder.

- correct.C: minor chages for specific checks