Feature/tilemap

I think TileMap is ready for review. 
There some UI features that I'd like to discuss to enable switching map types and setting/changing some params.

For now, default map type is the quantizeCircleMarkers.
To change map type, see 73 to 76: 
https://github.com/jthomassie/kibana/blob/feature/tilemap/src/kibana/components/vislib/visualizations/tile_map.js#L73-76
its unclear to me what n[1] and n[2] represent. Could you add some comments to explain how this pulls min and max values.