Backport to 7.8: Regression: original image data is no longer stored as-is

The original image data is no longer stored as-is when uploading an image. That means that several properties may/will be lost:

• the animation of animated GIFs will be lost
• EXIF data will be lost (i.e. the meta-data set by cameras or phones)

Steps to reproduce:
1. upload an animated GIF

Expected: the 'original' variant shows the animation
Actual: none of the variants shows the animation

The original image data should probably be left untouched, so the original data is always available (e.g. also to generate additional variants from later on).