Blender Git Loki

VSE: Free animation strip data if they are not visible

Previously we would only free animation strip data when doing final
renders. If not doing a final render or simply just playing back videos
in the VSE, we would not free decoders or non VSE cache data from the
strips.

This would lead to memory usage exploding in complex VSE scenes.

Now we instead use the dumb apporach of freeing everything that is not
currently visible.