added merge_fabricated_subsets() function

* The merge_subsets() function does not allow for the transfer of
centroid information or overall lnl. These need to be preserved for
lumping fabricated subsets back together at the end.
changed models to all
fixed bug with duplicated fabricated subsets

* There was a few bugs, one where the fabricated subsets would be added
to the list again, if they hadn't been analyzed and another with the
merged subsets lacking centroid, this now calls the
"merge_fabricated_subsets()" function to take care of that.
created add_centroid() function
ignore best_scheme files