MC momentum reconstruction for positive-charge particles

Currently, the p348-reco reconstruction code is such that the momentum reconstruction with Genfit works only for simulations performed with negative-charge particles (negative magnetic field)

I think the reason is that, probably, the tracking code is assuming that we have negative-charge particles, and hence the magnetic field is set in simu.h as:

 MAG_field = -1 * mcrunoption<double>("Magnet:MagnetMagY");

I tried with:

 MAG_field = fabs(mcrunoption<double>("Magnet:MagnetMagY"));

and this seems to work also for positive-charge particels.

@bbantoob may I ask you what you think about this?

This is closely related to closed issue #63 (closed)