Generalize Vision Depth Pipeline

Remove the depth / disparity pipeline from StereoVideo source and allow it to be applied to any source that lacks a Depth channel but has both Left and Right. This would allow FTL files with only Left and Right to be used with a vision node locally. If this entire process could be turned into an operator then reconstruct could also perform the disparity task.

It requires that source notifications return Frame objects rather than GpuMats.