New maps / new map data

[schlomm]

We should also add some data from CartoDb, more ArcGIS Server sources and services like www.mapbox.com
First and seconds are already supported by the included Leaflet.Vector Layer package: JasonSanford/leaflet-vector-layers#31
Maybe we have to switch to another one because of the issue: #1

[schlomm]

Some more useful things from ESRI: https://github.com/Esri/esri-leaflet