Add tracking for MQ Level 5 and/or prefers-reduced-motion?

[JamesCatt]

prefers-reduced-motion MQ shipped in FF63, but it's not tracked here. FF meta bug refers to the whole level 5 spec, so not sure what the preferred way to track it is.

Interaction MQs were tracked as a unit, which corresponds to the way caniuse & other browsers seem to have tracked it. Convention seems to be to track prefers-reduced-motion separately though.

caniuse: https://caniuse.com/#feat=prefers-reduced-motion
Edge: https://developer.microsoft.com/en-us/microsoft-edge/platform/status/mediaqueriesprefersreducedmotion/?q=prefers-reduced-motion
Chromium: doesn't seem to be tracked in platform status, but is being "actively worked on"
Webkit: shipped, but doesn't seem to be tracked

[chrisdavidmills]

I think it makes sense to track different types of media feature separately, as they do have different use cases and are being implemented separately in many cases. I'll add a row for prefers-reduced-motion

[chrisdavidmills]

I created a PR for this: #568

Do you fancy reviewing it to see if it looks OK?