Create an image registration worker

[arjunrajlab]

It would be helpful to have the option to register images, especially for time-lapse imaging. It would be good to have the option of doing control points and/or pystackreg for automated transformations. We could do this either as a docker plugin or a worker? Not sure if a worker would have sufficient control.

The multi-source specification is here:
https://girder.github.io/large_image/multi_source_specification.html

And there is an example of setting these values from histomicsTK:
https://github.com/DigitalSlideArchive/histomicstk-extras/blob/master/histomicstk_extras/RegisterImages/RegisterImages.py#L175-L193

If it is possible to do this within a worker, then we can have some mix of control points and pystackreg with certain frames skipped, depending. That would be relatively easy to implement.