fix(angular): add injectable decorator to fix injectable issues

packages/angular/src/providers/alert-controller.ts

@@ -1,8 +1,11 @@
+import { Injectable } from '@angular/core';
 import { AlertOptions } from '@ionic/core';
 
 import { ensureElementInBody, hydrateElement } from '../util/util';
 
 let alertId = 0;
+
+@Injectable()
 export class AlertController {
   create(opts?: AlertOptions): AlertProxy {
     return getAlertProxy(opts);

packages/angular/src/providers/app.ts

@@ -1,9 +1,13 @@
+import { Injectable } from '@angular/core';
 import { NavContainer } from '@ionic/core';
 import { hydrateElement } from '../util/util';
 
+@Injectable()
 export class App {
 
-  constructor(private element: HTMLIonAppElement) {
+  private element: HTMLIonAppElement;
+  constructor() {
+    this.element = document.querySelector('ion-app') as HTMLIonAppElement;
   }
 
   setTitle(title: string) {

packages/angular/src/providers/nav-controller.ts

@@ -1,3 +1,4 @@
+import { Injectable } from '@angular/core';
 import { NavOptions, PublicNavController, ViewController } from '@ionic/core';
 import { hydrateElement } from '../util/util';