STORAGEMODEL-288 adding json_field

this work is spread across:
* asi
* storagemodel
* smock
* integration-tests
STORAGEMODEL-288 fixing unpack_json
STORAGEMODEL-228 fixing pack_json
Finished release v0.6.25.

* release/v0.6.25:
  STORAGEMODEL-228 fixing pack_json
  STORAGEMODEL-288 fixing unpack_json
  STORAGEMODEL-288 adding json_field