Adding AddCovariance method

Adding AddCovariance method

// Adding systematic errors to the covariance:
//
// The systematic errors due to the misalignment and miscalibration are added to the covariance matrix
// of the tracks (not to the clusters as they are dependent):
// The parameters form AliTPCRecoParam are used AliTPCRecoParam::GetSystematicError
// The systematic errors are expressed there in RMS - position (cm), angle (rad), curvature (1/cm)
// The default values are 0.
//
// The sytematic errors are added to the covariance matrix in following places:
//
// 1. During fisrt itteration - AliTPCtrackerMI::FillESD
// 2. Second iteration -
//      2.a ITS->TPC   - AliTPCtrackerMI::ReadSeeds
//      2.b TPC->TRD   - AliTPCtrackerMI::PropagateBack
// 3. Third iteration  -
//      3.a TRD->TPC   - AliTPCtrackerMI::ReadSeeds
//      3.b TPC->ITS   - AliTPCtrackerMI::RefitInward