New parameter in CaloDataType (@vchekali)

Add isPhotonXGB parameter, to be used by CaloHypoEstimator to store result of new photon/pi0 separation classifier.
Cherry picked from !1348 (merged) in 2018-patches

• [2018-06-03 00:10] Validation started with lhcb-head#1873
• [2018-06-03 00:10] Validation started with lhcb-lcg-dev4#544
• [2018-06-03 00:11] Validation started with lhcb-clang-test#972
• [2018-06-03 00:12] Validation started with lhcb-gaudi-head-py3#173
• [2018-06-03 00:13] Validation started with lhcb-tdr-test#170
• [2018-06-03 00:13] Validation started with lhcb-lcg-dev3#544
• [2018-06-03 00:14] Validation started with lhcb-gaudi-head#1887

merged

mentioned in commit cc467633