added site_lnls to subset before splitting subset
changed to take the site likelilhoods
added site_lnls variable to subsets

* This will save a list of site likelihoods for use later if subset is
unanalyzable
added functionality to keep site lnl's in split subsets

* site_lnls need to be transferred with the split subset in the case
that it is unanalyzable by the chosen phylogeny program later. If the
subset is analyzable, the site likelihoods will be updated as they are
generated.