add "random vertex placement" to AddGenieEventsToArt module in v1_21 (archival)
Just before NOvA switched to art2 (and the vastly upgraded nutools v2), we did one last special study with GENIE events generated "standalone" rather than through the ART interface. We needed to "side-load" them into ART using the AddGenieEventsToArt_module, but unfortunately one of the features of that module wasn't
implemented in the v1_21 branch, random vertex placement (though it is in v2).
feature/jwolcott_addgenieevts_rndmvtx_v121, which implemented the feature, into
v1_21_branch so we have an archival copy of the code we used. Thanks!