SVG play/pause

I ran some numbers, and I think SVGs vs optimized PNGs for these basic shape images are basically the same size. Reducing use of the `image` mixin also reduces a decent amount of media queries, so size on the wire I think this is net smaller. Plus this eliminates the need for multiple sizes, and since we reuse some of these images at non-native sizes this should also render better.

Just wanted to start the conversation.