Add support for other trees

[chrzyki]

It might be nice to have other trees than only the Glottolog global tree. See, for example, D-PLACE. Low priority.

[SimonGreenhill]

Changed my mind on this -- yes, we should import and re-use DPLACE's functionality here if we can, e.g. https://d-place.org/phylogenys/gray_et_al2009?parameter=EA001

[SimonGreenhill]

...and this would be probably easiest implemented using @xotwang's https://github.com/cldf-datasets/dplacetrees