Make onFoo {} methods available directly on widgets and containres

[abreslav]

Instead of

                listView {
                    vgInstance onScroll {
                        onScroll { a,b,c,d ->  }
                        onScrollStateChanged { a,b -> }
                    }

have

                listView {
                        onScroll { a,b,c,d ->  }
                        onScrollStateChanged { a,b -> }
                }

Same for widgets