Tolerance for all image ratios

Created by: temparus

Currently, for images with aspect ratio 16:9 or 1:1, the aspect ratio is strictly enforced by the API without any tolerance. This is not very practicable as an image with 1 pixel row more in one direction will be rejected although Photoshop cropped with an aspect ration of 16:9.

We should have some tolerance for all aspect ratios.