Merge branch '1147-bluetooth-discovery' into 'master'

...ject/bramble/plugin/bluetooth/AndroidBluetoothPlugin.java

...amble/plugin/bluetooth/AndroidBluetoothPluginFactory.java

...oject/bramble/api/keyagreement/KeyAgreementConstants.java

...riarproject/bramble/plugin/bluetooth/BluetoothPlugin.java

...project/bramble/plugin/bluetooth/JavaBluetoothPlugin.java

briar-android/src/main/AndroidManifest.xml

...c/main/java/org/briarproject/briar/android/AppModule.java

...org/briarproject/briar/android/activity/RequestCodes.java

...ject/briar/android/keyagreement/KeyAgreementActivity.java

briar-android/src/main/res/values/strings.xml