And optionally show an error message, if libQuotient gets one. This
helps in certain rare situations where you just *Cannot* download
something. Before, NeoChat would just reset the image or video without
telling you anything but now there's a nice big error message telling
you what's wrong.
The video thumbnail is no longer hidden while loading. This makes it
look less buggy (like NeoChat forgot what the thumbnail was) while
loading a large video. To help with contrast, a slight background tint
is added.
