view different combinations of channels in parallel.

[JonasCF]

When loading images it would be useful to load different combinations of channels in parallel.
scrolling should then make all previews move in parallel and ROIs should show on all of them too.

It would be useful to see red channel at the same time as red + green.

Also when we choose all channels, I am afraid that Blue channel potentially can contaminate our signal with some filter settings in the microscope.