Added push notifications, FCM.

android/app/src/main/AndroidManifest.xml

@@ -7,6 +7,7 @@
     <uses-permission android:name="android.permission.WRITE_INTERNAL_STORAGE" />
 
     <application
+        android:name=".Application"
         android:label="Cake Wallet"
         android:allowBackup="false"
         android:fullBackupContent="false"
@@ -29,7 +30,6 @@
                 <category android:name="android.intent.category.LAUNCHER"/>
             </intent-filter>
         </activity>
-
         <meta-data
                 android:name="flutterEmbedding"
                 android:value="2" />

android/app/src/main/java/com/cakewallet/cake_wallet/Application.java

@@ -0,0 +1,21 @@
+package com.cakewallet.cake_wallet;
+
+import io.flutter.app.FlutterApplication;
+import io.flutter.plugin.common.PluginRegistry;
+import io.flutter.plugin.common.PluginRegistry.PluginRegistrantCallback;
+import io.flutter.plugins.GeneratedPluginRegistrant;
+import io.flutter.plugins.firebasemessaging.FlutterFirebaseMessagingService;
+import io.flutter.plugins.firebasemessaging.FirebaseMessagingPlugin;
+
+public class Application extends FlutterApplication implements PluginRegistrantCallback {
+  @Override
+  public void onCreate() {
+    super.onCreate();
+    FlutterFirebaseMessagingService.setPluginRegistrant(this);
+  }
+
+  @Override
+  public void registerWith(PluginRegistry registry) {
+    FirebaseMessagingPlugin.registerWith(registry.registrarFor("io.flutter.plugins.firebasemessaging.FirebaseMessagingPlugin"));
+  }
+}