Direct bibliography integration from glottolog

[SimonGreenhill]

Glottolog's various bibtex files allow for quick referencing, as they preserve the original keys. We should provide an easy way to do this, rather than duplicating bibtex files in data repositories.

[SimonGreenhill]

We currently have getEvoBibAsBibtex, so a similar function for getGlottologBibAsBibtex(...) would be really useful for the download phase. We have glottolog installed locally however, so we should just be able to query it.

[xrotwang]

To assemble the references of dryerorder, I used code looking up title, year and author using pyglottolog.fts.search. Maybe I should just write this up in a pyglottolog recipe.