[Windows] Perform pairing when reading/writing a secure attribute

Code has been added for Windows/WinRT to scan and connect to a BLE device without the need to first pair with the device outside of the Qt application. The behaviour is however still quite different from other platform with respect to secure characteristics. On other platforms, scanning, connecting and reading/writing unsecure characteristics can be done without pairing and as soon as a secure characteristic is read/written, the OS handles the pairing and the read/write succeeds. In the Windows/WinRT implementation, this does not happen automatically and an error is returned by Qt. It would be nice if Qt could start the pairing automatically and continue with the reading/writing.