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.
We had support for detecting aspect ratios and respecting them in the
render, but this allows people to not only see the aspect ratio in use,
but also override it with their own.
itsmattkc