Serialize objects on the way out of the hacked conductor helpers

Change-Id: I68e5463c91a41b4b6e8a42b54cbf5aa1fd2629ff
Communicate changed fields in primitive format

Change-Id: I188d1ffb2394fe54025dd63454dac2373514594c
Make Migration object correctly implement save

That means using changed fields and constructing updates.

Change-Id: I3d2ffa04d4e40b25de0c0d9d4c9c6d36a5928758