M1 demo fixes

A few small fixes noticed during m1 testing. To test:

 - Preview panel and main image viewer should zoom the image to fit when loaded, zooming small images above 100% if needed.
 - While dragging the channel slider in main image viewer, the input fields at either end should not show a red background.
 - "Full range" button should be disabled for 'double' pixel-type images in Preview and main image viewer.
 - The rendering def thumbnails in Preview panel should be same as Insight:
    - Owner of the image should be in blue.
    - Current rendering def should be outlined in blue when loaded and on click to select.

cc @chris-allan: 1 small method added to BlitzGateway image.getRenderingDefId()

--no-rebase