Configure caches to limit tiles by zoom level or image type

[xicesky]

At the moment, only layers can be configured to be limited to a certain zoomlevel range - i.e. via "bounds": { "low": 0, "high": 20 }
The same goes for the image type, which we can - at least - configure by redirection via "redirects": { "jpg": "png" }
But IMHO it should be possible to configure this for the cache, or specific caches in a multi cache setup: This would ensure that a tile of e.g. zoom level 100 will never be cached, but could still be rendered on-the-fly.

[rajanski]

+1