Operation: External API

allow Op[{body: "Great!"}, {additional: true}] to save merge.
make Op[] not require wrap like comment: {}
in tests, make Op[].model return the reloaded model!

Operation: Internal API

don't populate the form in #present context, we don't need it (only the representer goes nuts)
don't pass contract in validate, we have #contract.
abstract validate/success/fail into methods to make it easily overrideable.