How to link a HAPI server + dataset id to an observatory/spacecraft

[rweigel]

See the first two comments for the issue posted at hapi-server/servers#4

[jvandegriff]

Do we need more tags or metadata in the catalog to indicate membership in groups (or even sub-groups).

Could possibly relate to the interest in linking datasets that are related by time resolution.

[sandyfreelance]

Seems related to #118 and #78, I think all 3 should be solved as a bundle.