[IMP] component: introduce OwlEvent

Closes #485

doc/reference/component.md

@@ -567,11 +567,13 @@ A _business_ DOM event is triggered by a call to `trigger` on a component.
  }
 ```
 
-The call to `trigger` generates a [_CustomEvent_](https://developer.mozilla.org/docs/Web/Guide/Events/Creating_and_triggering_events)
-of type `menu-loaded` and dispatches it on the component's DOM element
-(`this.el`). The event bubbles and is cancelable. The parent component listening
-to event `menu-loaded` will receive the payload in its `someMethod` handler
-(in the `detail` property of the event), whenever the event is triggered.
+The call to `trigger` generates an `OwlEvent`, a subclass of [_CustomEvent_](https://developer.mozilla.org/docs/Web/Guide/Events/Creating_and_triggering_events)
+with an additional attribute `originalComponent` (the component that triggered
+the event). The generated event is of type `menu-loaded` and dispatches it on
+the component's DOM element (`this.el`). The event bubbles and is cancelable.
+The parent component listening to event `menu-loaded` will receive the payload
+in its `someMethod` handler (in the `detail` property of the event), whenever
+the event is triggered.
 
 ```js
  class ParentComponent {

src/component/component.ts

@@ -1,4 +1,5 @@
 import { Observer } from "../core/observer";
+import { OwlEvent } from "../core/owl_event";
 import { CompiledTemplate, QWeb } from "../qweb/index";
 import { patch, VNode } from "../vdom/index";
 import "./directive";
@@ -388,7 +389,7 @@ export class Component<T extends Env, Props extends {}> {
    */
   trigger(eventType: string, payload?: any) {
     if (this.el) {
-      const ev = new CustomEvent(eventType, {
+      const ev = new OwlEvent(this, eventType, {
         bubbles: true,
         cancelable: true,
         detail: payload

src/core/owl_event.ts

@@ -0,0 +1,15 @@
+import { Component } from "../component/component";
+
+/**
+ * We define here OwlEvent, a subclass of CustomEvent, with an additional
+ * attribute:
+ *  - originalComponent: the component that triggered the event
+ */
+
+export class OwlEvent<T> extends CustomEvent<T> {
+  originalComponent: Component<any, any>;
+  constructor(component, eventType, options) {
+    super(eventType, options);
+    this.originalComponent = component;
+  }
+}