LoKiCore : add new class Polarization

Cherry-picked from 2018-patches, see merge request !1188 (merged)

• [2018-03-26 00:11] Validation started with lhcb-clang-test#901
• [2018-03-26 00:11] Validation started with lhcb-gaudi-head-py3#104
• [2018-03-26 00:13] Validation started with lhcb-head#1798
• [2018-03-26 00:14] Validation started with lhcb-tdr-test#100
• [2018-03-26 00:19] Validation started with lhcb-gaudi-head#1812

merged

mentioned in commit 866b330e