Images in reports are too large

[janezd]

After merging #208, images in reports are too large.

To reproduce, try reporting a box plot.

I assume that WebKit treats all images as 72dpi. Perhaps adding zoom: 0.5; to css would fix it. Edit: yes, but only if the image was taken on high-dpi screen.

[PrimozGodec]

As agreed at the meeting, I merged #246. Anyway, as said, we will look at this one again, so I am reopening the issue.
As @markotoplak, I am also concerned that we skipped some possible cases.

I also see another problem (which was here already before) if I include a super big widget in the report image, the image sticks out of the report container when the report window is smaller. I think it could be fixed by updating the HTML so that the container div would not allow images to overflow (the image's max-width should not be wider than the container width). This solution can also solve problems with too-wide images on the retina without changing DPI.