Allow fitting Raw Image to window size

[Blackclaws]

Is your feature request related to a problem?

Right now when storing image files with high resolutions as opaque datasets and visualizing them they do not fit into the display area and get scrollbars associated with them. While this makes sense when wanting to view details in the images it is a bit problematic if the image in question is just an overview picture with high resolution that is best viewed as a whole.

Requested solution or feature

Add a toggle to fit/not-fit an image within the display area.

Alternatives you've considered

Scaling down the image myself or adding a "thumbnail" low-res version but that just duplicates data.

[axelboc]

The new Fit image toggle is now available on myHDF5 (and it's on by default):