Bug 933113 - Modify Pair/Unpair interface for Gaia being able to Pair/Unpair with only BD address, r=gyeh, sr=mrbkap

NFC handover is a mechanism for two devices to exchange their Bluetooth device
address with each other. Then one device would be initialize the Bluetooth
pairing process with received Bluetooth device address. However currently we
need a BluetoothDevice object for Pairing/Unpairing, but actually the address
of the Bluetooth device object is the only thing Gecko requires.