Add a ByteString -> IO ImageData function

[fgaz]

Since handling asset files is tricky, using file-embed could be a great way of bundling them. But we do not yet have a way of getting an image from a ByteString (what file-embed returns).

Ideally we'd have a makeImageFromData :: ByteString -> IO ImageData function that sets the src to a base64 representation of the image.
makeImage would also need to be renamed to makeImageFromUrl/makeImageFromPath, with a deprecated makeImage = makeImageFromUrl