major TRD reconstruction update

major TRD reconstruction update
- update clusterizer for flexible switch between methods to calculate
  r-phi cluster position. Currently the following methods are supported:
    - COG - center of gravity
      - LUT - look up table [default]
        - GAUS - gauss approximation [testing phase]
        - move position calculation related code from clusterizer to the
          cluster
            itself
            - steering options for cluster position calculation
              implemented at Reconstructor level.
                - user help via static method
                  AliTRDReconstructor::Options() function
                  - consistent pad row cross implementation in the
                    tracklet. Reference
                      radial position for pads crossing pad row is
                      recalculated based on z
                        cluster charge distribution.
                        - miscellaneous