Remove alphabetical sorting of contributing studies.
Useful links for contributing studies (References)
Merge pull request #250 from OpenTreeOfLife/contributing-studies-page

Adding useful links for contributing studies (References page)
Merge pull request #251 from OpenTreeOfLife/merge-otus-and-refresh

Merge otus and refresh
Updated docs/comments for to_nexson method.
Merge branch 'merge-otus-and-refresh' of github.com:OpenTreeOfLife/opentree into merge-otus-and-refresh