rendernodeparser: Parse images differently

rendernodeparser: Parse images differently

Instead of encoding the raw data, encode the full image to a PNG.
And instead of stuffing that encoding into a string, use a full
data: url.
And then remove the width and height properties, because they're now
implicitly included in the data.
And then change the parser to match.
And because the parser now parses regular urls on top of data: urls, we
can now load any random file.