Find and use img height/width before render

[wolfgangs-code]

If an image is local (on disk), AC should see its dimensions and embed that in the tag when rendering as to avoid https://web.dev/cls/

Checking dimensions of remote images should be off by default, but enable-able. This ensures performance when the host is on a low-bandwidth environment, and more importantly upholds that AfterCoffee never makes external connections by default.