Insert SVGs directly into DOM (instead of `<img src="...">`)

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I tried this earlier and the issue I ran into was that replacing the entire icon removed event listeners and the whole thing broke. That shouldn't be a problem any more though, and this unblocks the monochrome configuration option and allows the extension to ship 75% less icons (just the css-variables icons instead of all of latte, frappé, macchiato, and mocha).