Update definitions for mdJSON component system identifiers

[hmaier-fws]

Several acquisition elements contain multiple identifiers. For example, the platform class (#219):

• platformId: ( character ) "a unique identifier for the platform" default: short UUID
• identifier: { identifier } "unique identification of the platform"

In the above case, the platformId is an internal mdJSON identifier to reference reusable components. The similar definitions for the "platformId" and "identifier" could cause confusion. All references to internal (mdJSON) identifiers should be updated to: "a unique mdJSON system identifier..." to distinguish them from an ISO specified identifier object.

The following acquisition components require updates:

• [ ] eventId (#214)
• [ ] instrumentId (#215)
• [ ] objectiveId (#216)
• [ ] operationId (#217)
• [ ] planId (#218)
• [ ] platformId (#219)
• [ ] passId (#220)