Expose QBluetoothTransfermanager to QML

There should be an easy way to share data via Bluetooth in qml.
The QBluetoothTransfermanager API is a bit too complicated to expose it to QML. So I would propose to create a new class for that.

BluetoothTransferManager {
file: filename(s)
property running;
function start()
property status;
...
}