Ignore invalid DOI when creating a study.

Addresses #424. If someone enters an invalid DOI, or another URL
entirely, don't bother trying to retrieve its publication reference info
from CrossRef.org. Instead, create a blank study "from scratch" and
apply the DOI/URL exactly as entered.
typo
Merge pull request #124 from OpenTreeOfLife/ignore_invalid_doi_on_create

Ignore invalid DOI when creating a study