All versions of Face Recognition Application

* Fixed support for Android NDK r18, as gnustl has been removed * Make the image square, so it does not crash on phones with different aspect ratios - see: https://github.com/Lauszus/FaceRecognitionApp/issues/25 * Add double tap to flip camera gesture * Update Eigen to 3.3.5 * Update Gradle to 4.6 * Use Android SDK 28