WIP: Added kalman fit for pixel tracks with momentum estimate

This MR adds an algorithm which runs a Kalman filter for the VP hits only, with the possibility of using the momentum estimate from the pre-set first state of the track. It uses a v2::Track object as a container of the states and as an input. This is likely to evolve along with the track model. The kalman filter currently implemented in PrPixelTracking is obsolete by this algorithm, and it's planned to remove that piece of code there.

The parameters for the scattering are tuned, at the moment, on the result of the pattern recognition along with the detector simulation. This will require some more work with the help of the cheatedPR, and likely the parametrisation will need to be slightly more sophisticated. Nonetheless, pulls at the first measurement and the impact parameter do not look catastrophic, so it's a reasonable first version. The goal of this MR, however, is mostly to get this algorithm in the code quickly to complete the general track flow.