Ability to pre-process source frames

Users have asked for the ability to pre-process source frames, e.g. to adjust things like exposure, white balance, and maybe sharpening. In general, they want to adjust one frame and then be able to apply that to the rest of the source frames, before stacking. There might be infrequent cases where they only want to adjust one or a few frames, though.

We would need to be really thoughtful about the UX here, because this is starting to blur the lines between Editor and Library.