Compress images further

[danielsaidi]

When adding a 2.6MB HEIC file to a document, the resulting file becomes 6MB+, which about corresponds to the file size you get when you convert the HEIC file to JPEG on disc.

The image in question is 4032 pixels wide, which I think could be scaled down. We should at least provide an image setting that lets us set the max file size or dimensions, and scale down any images accordingly.