Use blocked scoped variables

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

examples/custom-controls.js

@@ -11,7 +11,7 @@ import OSM from '../src/ol/source/OSM.js';
  * Define a namespace for the application.
  */
 window.app = {};
-var app = window.app;
+const app = window.app;
 
 
 //
@@ -26,20 +26,20 @@ var app = window.app;
  */
 app.RotateNorthControl = function(opt_options) {
 
-  var options = opt_options || {};
+  const options = opt_options || {};
 
-  var button = document.createElement('button');
+  const button = document.createElement('button');
   button.innerHTML = 'N';
 
-  var this_ = this;
-  var handleRotateNorth = function() {
+  const this_ = this;
+  const handleRotateNorth = function() {
     this_.getMap().getView().setRotation(0);
   };
 
   button.addEventListener('click', handleRotateNorth, false);
   button.addEventListener('touchstart', handleRotateNorth, false);
 
-  var element = document.createElement('div');
+  const element = document.createElement('div');
   element.className = 'rotate-north ol-unselectable ol-control';
   element.appendChild(button);
 
@@ -57,7 +57,7 @@ inherits(app.RotateNorthControl, Control);
 //
 
 
-var map = new Map({
+const map = new Map({
   controls: defaultControls({
     attributionOptions: {
       collapsible: false