Create compatible style-spec for OpenLayers

Nobody has claimed this yet.

Although we support OpenLayers via [ol-mapbox-style][ol-mapbox-style] we don't show the user what styling rules are actually supported.

I suggest we create a spec for [ol-mapbox-style][ol-mapbox-style] we can merge into https://github.com/mapbox/mapbox-gl-js/blob/master/src/style-spec/reference/v8.json, this will then get rendered in the new UI, added in #607

Steps

- Create styles showing each styling properties in use
- I've made a start on this in https://github.com/orangemug/mapbox-gl-render-compare
- Decide on which properties are good enough to be considered supported by [ol-mapbox-style][ol-mapbox-style]
- They don't need to be pixel perfect but _good enough_, there is actually one case at the moment where [ol-mapbox-style][ol-mapbox-style] does a better job

[ol-mapbox-style]: https://www.npmjs.com/package/ol-mapbox-style

Review the Mapbox GL style-spec reference at src/style-spec/reference/v8.json and the existing examples in the linked mapbox-gl-render-compare project. Compare each styling property with ol-mapbox-style and decide which are sufficiently supported. Done means a compatible spec with representative styles that can be merged and rendered by the new UI described in #607.

Written by the indexing model from the issue text.