Physical AV extra data

[MTCam]

We should fix up physical AV smoothness handling (#735 ) so that it is only used when AV is ON. The extra data has a significant impact on our memory and communication volumes. The pattern of needing to add or use data items optionally keeps popping up (tseed, smoothness, etc). Maybe we can address this by adding an XV data structure or similar that makes it easier to stuff things like this into the code and add it to our interfaces.