Zooming on Small Images Should Fill Available Space

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

Zooming in on small pictures for more accurate labeling is made less useful by the fact that the original image size limits the size of the zoomed in area. With a fullscreen browser window I have lots of extra space, but when I zoom in on a small image I'm stuck looking at the zoomed in section through a frustratingly small area, requiring panning to move around, when there's plenty of space in the window to show the larger image.

**Describe the solution you'd like**
Zooming in on an image should increase the size of the image in the window as well, filling available space.