LoKiCore.functions: add (move from LoKiArrayFunctors) function PDGM (@belyaev)

Cherry picked from !1397 (merged) on run2-patches

• [2018-07-11 11:51] Validation started with lhcb-tdr-test#211
• [2018-07-12 00:13] Validation started with lhcb-lcg-dev3#583
• [2018-07-12 00:14] Validation started with lhcb-lcg-dev4#583
• [2018-07-12 00:15] Validation started with lhcb-head#1916
• [2018-07-12 00:16] Validation started with lhcb-gaudi-head#1928
• [2018-07-12 00:23] Validation started with lhcb-tdr-test#212
• [2018-07-12 00:47] Validation started with lhcb-gaudi-head#1928

merged

mentioned in commit 188366c9

mentioned in merge request !1719 (merged)