Set 'mtbmap-no' as an imagery source that uses 512px tiles

(closes #5179)

data/imagery.json

@@ -42137,6 +42137,7 @@
       "name": "MTBmap.no",
       "type": "tms",
       "template": "https://mtbmap.no/tiles/osm/mtbmap/{zoom}/{x}/{y}.jpg",
+      "tileSize": 512,
       "zoomExtent": [3, 14],
       "polygon": [
         [

data/update_imagery.js

@@ -96,6 +96,8 @@ sources.concat(whitelist).forEach(function(source) {
     if (source.id === 'Mapbox') {
         im.template = im.template.replace('.jpg', '@2x.jpg');
         im.tileSize = 512;
+    } else if (source.id === 'mtbmap-no') {
+        im.tileSize = 512;
     }
 
     if (source.type === 'wms') {