Make Style-brushes usable on custom layers

{"children":[{"type":"paragraph","children":[{"text":"When using a style-brush you cannot apply the desired effects very precisely. If you make the masked area visible during drawing it's difficult to evaluated the effects in many cases. If you use the style-brush freehanded you often have to erase wrong parts afterwards. This takes at least much time and still often remains unsatisfying. It's easier to produce a perfect mask first which then could limit the effects of the style-brush exactly to the mask's borders."}]}]}