added Bc_psi2SKKpi\,mm\=BcVegPy\,DecProdCut.dec

Hi, this is a decfile for Bc decay to psi2S(-> mu+ mu-) K+ K- pi+, similar to the EventType=14435002 but with psi(2S) and SR formfactor set.

The decparser gives a warning that the chosen EventType=14145005 has the same extra flag as few existing decay modes, but these have similar final state (charmonium->mumu + 3 hadrons). Possibly, the EventType could be chosen as 1414504X (charmonium + 3 hadrons and the same BCVHAD model), or even 141450[678]1 (extra flags 7,8,9 are unused so far), and user flag = 1 could correspond to 'BC_VHAD 1' parameter.