re-instate the grafted_supertree with user-friendly labels

[kcranston]

During the florida workshop, we had many requests for a phylogeny-only version of the synthetic tree with taxon names (i.e. grafted_supertree with taxon names instead of IDs). This seems to have disappeared from the output and from the html docs (although it is still mentioned in the readme).

[mtholder]

hmm. It is produced when I run the synth. Perhaps I culled it when producing the tar-ball for posting. I can look into that the next time that I post a synth.

I think that the tree at labelled_supertree/labelled_supertree_ottnames.tre would probably be of more use to users, though. That one has internal node labels.