Add MapBox Satellite layer. Fixes #318

js/id/renderer/background_source.js

@@ -45,3 +45,7 @@ iD.BackgroundSource.Tiger2012 = iD.BackgroundSource.template(
 iD.BackgroundSource.OSM = iD.BackgroundSource.template(
     'http://{t}.tile.openstreetmap.org/{z}/{x}/{y}.png',
     ['a', 'b', 'c'], [0, 18]);
+
+iD.BackgroundSource.MapBox = iD.BackgroundSource.template(
+    'http://{t}.tiles.mapbox.com/v3/openstreetmap.map-4wvf9l0l/{z}/{x}/{y}.jpg70',
+    ['a', 'b', 'c'], [0, 16]);

js/id/ui/layerswitcher.js

@@ -12,6 +12,10 @@ iD.layerswitcher = function(map) {
             name: 'OSM',
             source: iD.BackgroundSource.OSM,
             description: 'The default OpenStreetMap layer.'
+        }, {
+            name: 'MapBox',
+            source: iD.BackgroundSource.MapBox,
+            description: 'Satellite and Aerial Imagery'
         }, {
             name: 'Custom',
             source: iD.BackgroundSource.Custom,