Add ToolkitImage.getImage() method which loads an image with schema variant

Where should be a method which allows to load an image with resolution variants.

It is better handled by supplying a parameter when you create/get the image, such as:

Toolkit.createImage(URL, double... scales)
or
ImageVariantSchema myschema = new IVS(list of scales and suffixes);
Toolkit.createImage(URL, myschema);