[FIX] playground: update samples to make them work on firefox

Sadly, Firefox does not support yet static class fields, so we need to
use an equivalent, but slightly not as nice, syntax.

closes #335

tools/playground/samples.js

@@ -11,9 +11,9 @@ class Greeter extends Component {
 
 // Main root component
 class App extends Component {
-    static components = { Greeter };
     state = useState({ name: 'World'});
 }
+App.components = { Greeter };
 
 // Application setup
 // Note that the xml templates are injected into the global TEMPLATES variable.
@@ -58,7 +58,6 @@ class Counter extends Component {
 
 class App extends Component {
     state = useState({ flag: false, componentFlag: false, numbers: [] });
-    static components = { Counter };
 
     toggle(key) {
         this.state[key] = !this.state[key];
@@ -68,8 +67,8 @@ class App extends Component {
         const n = this.state.numbers.length + 1;
         this.state.numbers.push(n);
     }
-
 }
+App.components = { Counter };
 
 const qweb = new owl.QWeb(TEMPLATES);
 const app = new App({qweb});
@@ -217,7 +216,6 @@ class DemoComponent extends Component {
 }
 
 class App extends Component {
-    static components = { DemoComponent };
     state = useState({ n: 0, flag: true });
 
     increment() {
@@ -228,6 +226,7 @@ class App extends Component {
         this.state.flag = !this.state.flag;
     }
 }
+App.components = { DemoComponent };
 
 const qweb = new owl.QWeb(TEMPLATES);
 const app = new App({ qweb });
@@ -332,20 +331,18 @@ class ToolbarButton extends Component {
     }
 }
 
-class Toolbar extends Component {
-    static components = { ToolbarButton };
-}
+class Toolbar extends Component {}
+Toolbar.components = { ToolbarButton };
 
 // Main root component
 class App extends Component {
-    static components = { Toolbar };
-
     toggleTheme() {
         const { background, foreground } = this.env.themeContext.state;
         this.env.themeContext.state.background = foreground;
         this.env.themeContext.state.foreground = background;
     }
 }
+App.components = { Toolbar };
 
 // Application setup
 const themeContext = new Context({
@@ -497,7 +494,6 @@ class TodoItem extends Component {
 // TodoApp
 //------------------------------------------------------------------------------
 class TodoApp extends Component {
-    static components = { TodoItem };
     state = useState({ filter: "all" });
     todos = useStore(state => state.todos);
     dispatch = useDispatch();
@@ -537,6 +533,7 @@ class TodoApp extends Component {
         this.state.filter = filter;
     }
 }
+TodoApp.components = { TodoItem };
 
 //------------------------------------------------------------------------------
 // App Initialization
@@ -1014,23 +1011,20 @@ class Navbar extends owl.Component {}
 
 class MobileSearchView extends owl.Component {}
 
-class ControlPanel extends owl.Component {
-    static components = { MobileSearchView };
-}
+class ControlPanel extends owl.Component {}
+ControlPanel.components = { MobileSearchView };
 
 class AdvancedComponent extends owl.Component {}
 
-class FormView extends owl.Component {
-    static components = { AdvancedComponent };
-}
+class FormView extends owl.Component {}
+FormView.components = { AdvancedComponent };
 
 class Chatter extends owl.Component {
     messages = Array.from(Array(100).keys());
 }
 
-class App extends owl.Component {
-    static components = { Navbar, ControlPanel, FormView, Chatter };
-}
+class App extends owl.Component {}
+App.components = { Navbar, ControlPanel, FormView, Chatter };
 
 //------------------------------------------------------------------------------
 // Responsive plugin
@@ -1188,13 +1182,13 @@ class Counter extends Component {
 
 // Main root component
 class App extends Component {
-    static components = {Card, Counter};
     state = useState({a: 1, b: 3});
 
     inc(key, delta) {
         this.state[key] += delta;
     }
 }
+App.components = {Card, Counter};
 
 // Application setup
 const qweb = new owl.QWeb(TEMPLATES);
@@ -1298,7 +1292,6 @@ class SlowComponent extends Component {
 class NotificationList extends Component {}
 
 class App extends Component {
-    static components = {SlowComponent, NotificationList};
     state = useState({ value: 0, notifs: [] });
 
     increment() {
@@ -1311,6 +1304,7 @@ class App extends Component {
         }, 3000);
     }
 }
+App.components = {SlowComponent, NotificationList};
 
 const qweb = new owl.QWeb(TEMPLATES);
 const app = new App({ qweb });
@@ -1492,7 +1486,6 @@ class Window extends Component {
 }
 
 class WindowManager extends Component {
-  static components = { Window };
   windows = [];
   nextId = 1;
   currentZindex = 1;
@@ -1538,15 +1531,16 @@ class WindowManager extends Component {
     ev.target.style["z-index"] = w.zindex;
   }
 }
+WindowManager.components = { Window };
 
 class App extends Component {
-  static components = { WindowManager };
   wmRef = useRef("wm");
 
   addWindow(name) {
     this.wmRef.comp.addWindow(name);
   }
 }
+App.components = { WindowManager };
 
 const qweb = new owl.QWeb(TEMPLATES);
 const windows = [