Improvements to image viewer sizing options

When an image resource/asset, is opened, it is currently always displayed at 100% size. This can be shrunken by clicking "Fit to Screen", but this must be done for each image individually and must be done again if the window is resized.

Suggestions

• Provide an option to use "Fit to Screen" by default. (Possibly as a new option that is similar to a printer's "Reduce to Margins" option: Use "Original Size" if the image is smaller than the screen, but use "Fit to Screen" if the image is larger than the screen)

• Provide an option for live-fitting, where the image resizes with the window