Implements the following:
- Sequences have pixel aspect ratios that work in tandem with footage PARs
to render footage correctly. Viewer and export also acknowledge PARs
- Sequences can have interlacing settings. This doesn't do anything yet,
eventually the renderer will need to interlace/deinterlace/reinterlace
appropriately in order to conform all the footage to the sequence. Export
acknowledges interlacing, but this only affects metadata, not the image.
itsmattkc