Android 6 no longer allows access to the local Bluetooth address. `BluetoothAdapter.getAddress()` now returns a fixed value. This will break our ability to give our address to contacts so they can connect without performing discovery. https://developer.android.com/intl/ko/about/versions/marshmallow/android-6.0-changes.html#behavior-hardware-id The plugin still uses BluetoothAdapter.getAddress(), it's only `TestingActivity` and `CrashReportActivity` that look at the value in `Settings.Secure`. we need to add a method (maybe in `AndroidUtils`?) for getting the value from the adapter, checking whether it's valid, getting the value from `Settings.Secure` if it's not, and throwing an exception if there's not a valid address there either.