Fasten viewer opening by showing a lower quality picture when available

[artonge]

Is your feature request related to a problem? Please describe.

The Viewer can take a bit of time to open, as it loads the files before showing anything.

Describe the solution you'd like

• We could show the UI before having the file loaded (darken the view faster) as the loader icon is not really visible.
• We could also use a smaller version of the file if it is available. Maybe by passing an element or a size to use.