Update package name to mozilla.fenix.

app/src/main/AndroidManifest.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
-    package="org.mozilla.fenix">
+    package="mozilla.fenix">
 
     <application
         android:allowBackup="true"

app/src/main/java/mozilla/fenix/MainActivity.kt

@@ -2,10 +2,11 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-package org.mozilla.fenix
+package mozilla.fenix
 
 import android.support.v7.app.AppCompatActivity
 import android.os.Bundle
+import org.mozilla.fenix.R
 
 class MainActivity : AppCompatActivity() {
 

app/src/main/res/layout/activity_main.xml

@@ -7,7 +7,7 @@
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    tools:context="org.mozilla.fenix.MainActivity">
+    tools:context=".MainActivity">
 
     <ImageView
         android:layout_width="wrap_content"