Create data structures for active fields

[gold2718]

The main data structures needed are:

• Field Info: All information about a field that is independent of how it will be processed as a diagnostic quantity. This is essentially the same information contained in a CCPP entry for the field. Other information includes:
  • sampling_seq: The frequency with which this field is sampled (default is once per time step).
• Process Info: All information about how the field will be collected and processed for output.