Add way for adapters to compose resource URLs.
Get API adapters via a service manager. Make sure adapters do not preserve state.
Remove vestigial methods from API manager.
Make various changes to API adapter.

- getApiUrl() should return absolute URLs.
- Add helper method to get API adapters from within an adapter.
- Begin conversion to JSON-LD starting with RDF model.
Merge branch 'develop' into resource-ref
Prevent similarly named resources from referencing the same adapter.
Reference related resources instead of serializing them.
Use resource name instead of adapter class to differentiate resource entities.
Use a JSON serializable DateTime for resource representation.
Remove tests.
Merge branch 'develop' into resource-ref
Merge branch 'resource-ref' into develop