CTPPS: x-to-xi interpolation
Created by: forthommel
This PR introduces the horizontal displacement/longitudinal proton momentum loss (aka x-to-xi) interpolation for pre-TS2 2016 data taking.
It relies on a set of conversion curves obtained from the linearised proton transport equation parameterising the beamline lattice (see these slides).
The fill-by-fill Roman pots alignment (based on the matching of track origin distribution with respect to dedicated "alignment runs" ; see here) is also applied upstream to the interpolation.
Several lookup-tables are introduced to ease the code readability.
