Replace goog.events.Event/EventTarget system with our own

This also removes goog.events.listen, goog.events.unlisten,
goog.events.unlistenByKey and goog.events.BrowserEvent.

src/ol/events/event.js

@@ -0,0 +1,51 @@
+goog.provide('ol.events.Event');
+
+
+/**
+ * @constructor
+ * @param {ol.events.EventType|string} type Type.
+ * @param {Object=} opt_target Target.
+ */
+ol.events.Event = function(type, opt_target) {
+
+  /**
+   * @type {boolean}
+   */
+  this.propagationStopped;
+
+  /**
+   * @type {string}
+   */
+  this.type = type;
+
+  /**
+   * @type {Object|undefined}
+   */
+  this.target = opt_target;
+
+};
+
+
+/**
+ * Stop event propagation
+ */
+ol.events.Event.prototype.preventDefault =
+ol.events.Event.prototype.stopPropagation = function() {
+  this.propagationStopped = true;
+};
+
+
+/**
+ * @param {Event|ol.events.Event} evt Event
+ */
+ol.events.Event.stopPropagation = function(evt) {
+  evt.stopPropagation();
+};
+
+
+/**
+ * @param {Event|ol.events.Event} evt Event
+ */
+ol.events.Event.preventDefault = function(evt) {
+  evt.preventDefault();
+};