Pin the NCB segment onto th calo exit

First attempt to reduce the beam background by adding a new constraint to the NCB segment. Introduce the additional constraint that the particle is roughly horizontal and crossed the calorimeter at z=0 roughly at the same height. This constaint drastically reduces the number of built NCB segments (cf. plots below - back is the current release and red are the patched distributions). Plots have been produced using one file from the heavy ion data-taking.

Tagging: @wlampl, @ekay, @pscholer, @calpigia, @verducci