Auto scale large images according to size

Review Request #8392 — Created Sept. 8, 2016 and submitted — Latest diff uploaded

Information

Review Board
release-3.0.x

Reviewers

Previously, we scaled images that contained @2x or @3x in their
filenames. For images that do not contain those hints, we now scale them
to the highest scaling factor less than or equal to 1 that allows the
most of the image to be shown.

Tested with a very large image and saw that it was scaled correctly in
image diff and single image mode.