[no-redundant-role] allow disabling for certain elements

Currently this rule reports on <ul role="list"> because it's not redundant for certain cases, namely with list-style: none in Safari; see https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/list-style#accessibility and https://webkit.org/b/170179#c1.

There's also a bug with <img> that references SVG in VoiceOver; see https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/img#identifying_svg_as_an_image. This means that <img src="foo.svg" role="img"> is not redundant.

I think there should be an option to allow certain elements, such as ul and ol. I'm less sure about img, and perhaps role="img" should only be allowed if the src points to SVG, but I'd be happy if it just blanket-allows <img role="img">.