Changes

'''BluetoothAdapterEvent''' is carried as the argument of [https://wiki.mozilla.org/B2G/Bluetooth/WebBluetooth-v2/BluetoothManager#onadapteradded manager.onadapteradded] and [https://wiki.mozilla.org/B2G/Bluetooth/WebBluetooth-v2/BluetoothManager#onadapterremoved manager.onadapterremoved] event handlerhandlers. Applications can know whether the added/removed adapter is default adapter, and get the added [https://wiki.mozilla.org/B2G/Bluetooth/WebBluetooth-v2/BluetoothAdapter BluetoothAdapter] object and knows whether or the added adapter is default address of removed adapter.