Refactors data product management to support registering data products

- Changes dataset registration to use data product identifiers and data product metadata.
- Changes dataset management to use data product identifier for registration
- Removes print statements in data product mgmt
- Registers child data products during creation
- Removes any support for child product activation, not used, not desired nor required.
- Updates URL for erddap download
Fixes PyDAP tests
Merge pull request #1337 from lukecampbell/erddap

ERDDAP support for Data Product Registration