Preserve BEAST-style annotations

[josephwb]

Brought up by @mmatschiner. BEAST-style annotations are not preserved when editing the tree (e.g., pxrmt).

Example tree:
tree TREE1 = ((1[&dmv={0.1}],2[&dmv={0.2}]),3[&dmv={0.3}])[&dmv={0.1}]:0.0;

More standard node labels like )something are preserved.

So this has to do with differently treating things like )something as a 'name' while )[something] is a 'comment' (mentioned here). Fix seems relatively easy, although with some tree edits the annotations may need to be changed (e.g. edge lengths). For a first pass just make sure things make it through.