Time with basic GeoPose JSON encodings

[jerstlouis]

Is validTime only supported for Advanced GeoPose with those URL-like parameters? (see also #69, in my own opinion, this unnatural JSON syntax is a show-stopper)

Could the validTime and frameSpecification simply be added to the basic YPR / Quaternion GeoPoses, as separate conformance classes adding additional properties, rather than defining completely different schemas for these additional capabilities?

The steep jump in complexity to the more advanced GeoPose encoding targets and complete disconnect from the basic ones is likely to inhibit their implementation, including any version supporting time.

Related to #48 and #50. I would personally consider this an essential capability.