Moves the metadata about coverages into the object store

- Adds new method to dataset management to deal with latest data (and
  changes).
- Updates ingestion and dataset management to use the object store for
  metedata, avoids loading a coverage at all cost for metadata.
- Updates visualization and data product mgmt to use new format.
- Test(s)
Removes get_last_update
Fixes dmend2end tests
Merge pull request #1452 from lukecampbell/bounds

Moves the metadata about coverages into the object store