Add a way to revert to the old UI

So many of your user base absolutely despises this awful forced update, me included, and it would be much appreciated if there was a way to revert to the old ui, so that people who prefer the new ui can keep using it, and everyone who hates it can disable it. Personally I dislike the ui so much that I have uninstalled discord mobile, and I won’t be reinstalling until there’s a fix.