Make plugins aware of SDI field mode
With data-playback largely in place (#2430 (closed)), we can no longer change the field mode on the fly: its fixed in the recorded images. Also, I think it's not a good idea to be able to do that.
Instead, plugins that we intend to operate on SDI video should be made aware of the field mode so that they can do the right thing, automatically.
Plugins that need awareness are:
- Surface reconstruction
- Tag tracker
Overlay renderer[Edit: seems to work fine, with the correctly scaled image geometry.]