Changes bicon() to use the builtin 515 feature

[Exxion]

Obviously DNM until we're on 515. 515 makes this Just Work. It's clientside and even includes overlays (though not vis_contents, which may or may not be a bug). Includes a couple hacks to ensure it works in edge cases. We could finally add examine icons back to humans with this. They never actually worked properly before, but they do with this. I should probably also excise all other uses of icon2base64() as well but I haven't yet

Just opening because I want to remember it and also clean up my local copy