Use blocked scoped variables

In addition to using const and let, this also upgrades our linter config and removes lint (mostly whitespace).

examples/preload.js

@@ -4,12 +4,12 @@ import TileLayer from '../src/ol/layer/Tile.js';
 import BingMaps from '../src/ol/source/BingMaps.js';
 
 
-var view = new View({
+const view = new View({
   center: [-4808600, -2620936],
   zoom: 8
 });
 
-var map1 = new Map({
+const map1 = new Map({
   layers: [
     new TileLayer({
       preload: Infinity,
@@ -23,7 +23,7 @@ var map1 = new Map({
   view: view
 });
 
-var map2 = new Map({
+const map2 = new Map({
   layers: [
     new TileLayer({
       preload: 0, // default value