consolidate redundant load-JSON code
consolidate redundant dump-JSON code
tests for models functions (labels_vals,load/dump,formprep/post)
functions and UI to indicate how document model differs from repo's

Basically, indicate to the user whether the model definitions
in the Repository's 'ddr' repo are a different version from the
one used to prepare the document, and whether fields will be
added or removed when editing.
- Indicate whether model definitions in 'ddr' repo are
  newer/older than the document.
- Indicate whether model definitions in 'ddr' repo have added
  or removed fields from the POV of the document.