Image viewer bugs

[phyy-nx]

Reported by Mark Hilgart @ Argonne:

"A few minor bugs to report from the phenix dev-2776 version:

1. We may add an option to start the viewer in the mean function mode. Sending display=mean does affect the displayed image, but the “image” button is still selected instead of “mean”.

2. When launching the DIALS image viewer with the “kernel_size=5,5” option, it reports back that the parameter was changed, but it doesn’t look like it takes effect.

3. We passed an image on the command line, and that image was loaded. But then choosing a new image from the “load image” button didn’t display that second image. The second filename was added to the image dropdown."