feat(app): add app module

src/modules/app.ts

@@ -0,0 +1,12 @@
+import { Manifest } from '../models';
+import { Navigator } from './navigator';
+
+export class App {
+  getManifest(): Promise<Manifest> {
+    return new Promise((resolve, reject) => {
+      const request = Navigator.navigator.mozApps.getSelf();
+      request.onsuccess = () => resolve(request.result.manifest);
+      request.onerror = () => reject(request.error);
+    });
+  }
+}