New functors for estimation of helicity angle

This MR implements new functors for the estimation of the cosine of particle helicity angle. These functors were required in lhcb-dpa/project#221.

Two definitions of the helicity angle were implemented:

• The angle between the particle's momentum vector and its grandparent's momentum vector in the parent's rest frame (MC_COSTHETAH, COSTHETAH).
• The angle between the particle's momentum vector in the mother rest frame and the mother's momentum vector in the lab frame (MC_COSTHETA, COSTHETA).

The implementation of the helicity angle functors relies on the new boost functor, which transforms the first argument (four-vector) into the frame, where the second argument (four-vector) is at rest.

Goes with DaVinci!1040 (merged).

FYI: @jzhuo @adeoyang @amathad @erodrigu