Whitespace fixes
Don't output timestamp_precision if it is the default.
Add xsi type for COA Stage vocab.
Default to using HighMediumLow if no other VocabString type is provided to Statement
Don't enforce particular VocabString subclasses
Reorder COA fields to match schema
Add ParameterObservables to COA

Also clean up some duplicate code caused by Shayne and I accidentally
working on the same thing.