Skip creation of zoom,etc, callbacks in ImageView

This increases the performance substantially, at least for small videos. At least in other contexts, this also solves a weird memory problem https://github.com/timholy/ImageView.jl/issues/32. But my tests with VideoIO suggest the memory usage slowly grows over time. I'm not sure why that's happening.

Presumably the best solution is to pass the whole movie to ImageView as an object, so if you don't want to merge this, that's fine.