[not ready] add tiles option for remote sources

See https://github.com/mapbox/mapbox-gl-js/pull/697
Questions:
* Should we rename `minZoom` and `maxZoom` everywhere to `minzoom` and `maxzoom` to match tileJSON?
* Should we add more specific options rather than just wildcarding it for tileJSON things like `attribution`, `center`, `bounds`? (We probably should if we modify GL to do something with those...)