Fixes for new data

Fixes for issues after merging #362. See also #149.

Deployed to staging, see:

- author and title in views, e.g. http://staging.api.lobid.org/resource?id=HT002189125
- multiple isPartOf in views, e.g. http://staging.api.lobid.org/resource?id=BT000107425
- URN queries, e.g. http://staging.api.lobid.org/resource?id=urn:nbn:de:101:1-201210094953
- resource by author, e.g. http://staging.api.lobid.org/resource?author=118580604
- by author & set, e.g. http://staging.api.lobid.org/resource?author=108554600&set=NWBib