LPD DARKS also save paths, don't copy old constant files

Same thing as for AGIPD.  Proposing to save this alongside the module mapping (if we're creating
YAML files per module anyway).  Note that I had to add "cap" and "qm" layers to old_const and
old_mdata; there's probably only one element in each, so the dictionary is overkill, but as we loop
over both, this would otherwise break if we ever have more than one of either...