QRCode Scan: implement embedded qr code scanner

This patch implements the embedded QR Code Scanner. Ring does not
need a third-party application to scan codes anymore.
It relies on a new dependency: com.journeyapps:zxing-android-embedded

Change-Id: I3097ed6302d8c3314cb665cfed6ab34e9dfb4ba0
Tuleap: #558
diff --git a/ring-android/app/src/main/AndroidManifest.xml b/ring-android/app/src/main/AndroidManifest.xml
index e02ceab..d3799c2 100644
--- a/ring-android/app/src/main/AndroidManifest.xml
+++ b/ring-android/app/src/main/AndroidManifest.xml
@@ -255,6 +255,12 @@
                 <category android:name="android.intent.category.DEFAULT" />
             </intent-filter>
         </activity>
+        <activity android:name=".client.QRCodeScannerActivity"
+            android:screenOrientation="fullSensor"
+            android:stateNotNeeded="true"
+            android:theme="@style/zxing_CaptureTheme"
+            android:windowSoftInputMode="stateAlwaysHidden">
+        </activity>
 
         <service
             android:name=".service.LocalService"