Display SVG file and diff not as plaintext but as images

### Describe the feature or problem you’d like to solve
When I look at commit content in some repos, i see different commits with svg files added or modified, and the problem is that I can't see what's different before and after the modification or how looks like the file... I don't have any other solutions that open the file with the default app (but I can't see the older version...) :(

### Proposed solution
As for images diff, display before and after versions and the 4 widgets like "Onion skine", "Difference", etc.
Perhaps see as plaintext is useful too, so maybe the default view like image with the ability to change to plaintext view would be good.

This behavior will be resumed like that:
- Open commit content
- Click on a svg file
- See immediatly rich diff like other normal images (png, jpeg).
- Use the 4 widgets to see more details of the diff