Changing asset via command

Hi @mmotov,

I'll show you how I did it, it's easier to understand.

When capturing the value of the image I define it in the same way, but below I do some checks to know if the element is a background or not. 

editor.Commands.add("open-assets", {
    run(editor, sender, opts = {}) {
        var image = $("#img-file").val();
    
        opts.target.set("src", image);

        if (opts.target.attributes.type == "image") {
            if (image) {
                opts.target.set("src", image);
            }
        } else {
            if (opts.target.getStyle()["background-image"] == undefined) {
                var background = `url("${image}")`;
            } else {
                var background = opts.target.getStyle()["background-image"] + `url("${image}")`;
            }

            opts.target.addStyle({
                "background-image": background
            });

            editor.trigger("component:toggled");
        }

        editor.Commands.stop("open-assets");
    }
});