- Implementing Central task for filtering the ESD friends:

- Implementing Central task for filtering the ESD friends:
    - keeping only 1% of the whole sample, randomly selected

- Adding the setting/getting of the "skip" bit (bit 23) for AliESDfriendTrack/AliESDfriend
  during the filtering
    - AliESDfriendTrack --> to allow to have the logical or between tracks from different tasks
      when adding a "dummy" friend track (when not selected by the filter)
    - AliESDfriend --> to be able to disentagle between ESDfriends added because
      selected, or added as "dummy" ones when not selected

- Corresponding changes in AliAnalysisTaskFilter/AliESDHandler and in the
  example filtering tasks

- Removal of AliAnalysisFilterSTEER:
  - the 1% selection is now done in AliAnalysisFilterSteer
  - the pt selection should be handled in separate detector-specific tasks