Renaming clades

[mortonjt]

Right now, the y_i renaming of internal nodes is a bit jarring.
Perhaps we should enable renaming of only internal nodes that don't have names with something like clade_i.

The one thing to watch out for is internal node duplicates generated from tax2tree.

[mortonjt]

One final comment

1. This function will be compatible with the output of tax2tree that will enable annotation of internal nodes
2. This function will eventually deprecate rename_internal_nodes