Fix wrong LoKi MC functors
As discussed here: !3537 (comment 5534027) LoKi MC algs MCMAXTREE and MCMINTREE don't do what the documentation says they do. As @dathomps discovered, they multiply the value of a functor for every mc particle in the mc tree. They should find the max or min. LoKi algs exist to do this, so this MR fixes up the LoKi functors to use the right algorithms.