Limit side panels width

[mpizenberg]

If an image name or a class name is too long, the side panel width grows too much. Find a way to limit width of side panels.

[mpizenberg]

From ACM MM18 review:

When filenames are long and images are big, the panel on the right side that lists the image files covers the image hence interferes with annotation)

[mpizenberg]

From ACM MM18 review:

The image names on the right side sometimes cover the image as shown in Fig. 1, which makes that part of the image invisible and cannot be annotated properly.