GVoice Callback

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v0.4.2
1. Fix login issue for Android 4.0 ICS
2. Provide more accurate error messages when possible
3. Fix WaitForCallback layout

v0.4.0
Updated to use the new Google Voice interface. If log in hangs, please try killing and restarting the app again a few times.

v0.3.0
1. Register as a dialer and allow tablets (without native telephony) to install the app
2. Auto answer support for Android 8.0 Oreo