Android: Say hello to gradle!

Switching from Ant to Gradle brings lots of advantages:
 - it is way faster when rebuilding (25-50% faster than ant).
 - it enables first class Android Studio integration.
 - adding Android Extras libs (e.g. Google Play services, OBB, etc.) to
   your project is now painless.

[ChangeLog][Android] Added Gradle support to build the APK.

Change-Id: Iee492954f8ffb2c22e6ab14a8a25faf644de9a51
Reviewed-by: Daniel Teske <daniel.teske@digia.com>

src/plugins/android/androidsettingswidget.h

@@ -91,6 +91,7 @@ private slots:
     void dataPartitionSizeEditingFinished();
     void manageAVD();
     void createKitToggled();
+    void useGradleToggled();
 
     void checkGdbFinished();
     void showGdbWarningDialog();