Add support for exporting annotated phylogenies

This PR adds a button to phylogenies that allow them to be exported. Closes #226.

WIP:

[x] The output includes a bunch of extra characters at the start of the file -- maybe the Unicode BOM? We need to get rid of those.
[ ] Currently, this exports the entire Newick file, which is fine for the phylogeny view. For the phyloref view, however, we only want to display that specific phyloreference. Our current code filters out the other labels when drawing the phylogeny -- it might be worth looking at phylotree.js and seeing if there is some other way to hide internal node labels from both display as well as the Newick export.
[ ] We also want to distinguish between expected phyloreferences (as labeled in the phylogeny) and resolved phyloreferences (as determined by reasoning). Our plan in #226 is to leave expected phylorefs as-is (e.g. Alligatoridae) and to add either phyloref_ or reasoned_ as a prefix when the node was found by the reasoner (e.g. phyloref_Alligatoridae or reasoned_Alligatoridae).

phyloref / klados