MAPv3.1/temporal-related indexing fixes (refs #7704)

* Validation: MAPv3.1 temporal has to act like date based on API definition
* Readd enrich_date (temporal) enrichment to NYPL/MWDL
Merge pull request #33 from dpla/7704-mwdl-temporal

MAPv3.1/temporal-related indexing fixes (refs #7704)