Fix for multi-dex on Android 4.x

While Air 25 adds multi-dex support, the non-primary DEX files are not loaded on Android < 5 devices.

To fix this, simply add the following to your <manifestAdditions>

<application android:name="android.support.multidex.MultiDexApplication">

While the Air docs say the android:name element cannot be changed, the docs are incorrect.