Fitter & Calibrator (was ACTS-546)

Original author Andreas Salzburger @asalzbur

(1) Payload pattern:

In order to feed the {{KalmanFitter::typename calibrator_t}} with the right conditions data, we expand the {{fit(...)}} interface with a {{template }}.

For the {{Acts}} version, this can be a {{VoidConditionsData}} object.

Q: Why then not change to a general payload pattern (i.e. also for Surfaces regarding Alignment)?

(2) PropagatorOptions<> pattern:

Move {{PropagatorOptions<Actions,Aborters>}} outside the {{fit(..)}} call, hence the {{calibrator_t}} will be created at this stage and can connect to the conditions database. The {{calibrator_t}} instance then would have the right conditions data.