Feature: nanovg allow drawing on different levels #525
Description
As discussed before: sometimes it's wanted to be able to draw something on top of something else within the same context but after certain operations (ie. a parent to draw on top of its child widgets).
Right now there is only onNanoDisplay() that draws on a base level, but suggested is to have a onNanoDisplayLayer() where there could be an argument to draw on another level as well.