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 - to production]
- 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