Show labels for subtree root nodes
Show labels for subtree root nodes

This commit is related to the recent PR #1501 which hid (non-aa) labels
depending on their in-view tip-fraction. Here if the label is on the
root of a subtree then we always show it (unless the label is "aa" as
these can be very long).

nextstrain/auspice,nextstrain/auspice,nextstrain/auspice