Template VPTrackMonitor on fit node type

Enables VPTrackMonitor to run with PrKalmanFitResult and PrFitNode. Depends on !2786 (merged) which fixes a bug in unbiasedState() function for LHCb::FitNode in master (thanks @jadevrie).

I attach two comparisons of all variables the monitor saves in a tuple. The first one is between the current master and this MR using results from TrackMasterFitter, i.e. using LHCb::FitNode and LHCb::TrackFitResult - all histograms are the same. The other is between TrackMasterFitter and PrKalmanFilter in this MR. Note that the comparison between the current master and this MR does not include the bug fix for unbiasedState as it is not merged yet.

master_vs_mr.pdf tmf_vs_prkf.pdf

Here you can see the minimal option files I used to run the monitor. The TrackMasterFitter was configured to not add default reference nodes and use parametrized scattering to make it more similar to how PrKalmanFilter works.

VPTrackMonitorOpts.py VPTrackMonitorOpts_PrKalman.py

@ausachov, @freiss, @hcroft

Addresses Alignment#16