Draft: Create transient DataHeaderForm class
Add a transient DataHeaderForm class that is a small modifiction of the persistent DataHeaderForm. Create a new DataHeader class that will interact with the transient DataHeaderForm. Add converters for the new classes.
This MR is mostly for discussion of work in progress. Commits here may end up being thrown away and replaced.
TODO: [ ] Fill out interaction between new DataHeaderForm and DataHeader [ ] Remove old DataHeader [ ] Work though AthenaPool actions