Add discovering for BLE devices on Windows

BLE devices are supported in Windows 8 and above. Windows has not
public API to discovering/pairing of BLE devices. A user shall do
it by means of standard "bluetooth" application which are inbox into
Windows. Only after that there is an opportunity to display the
discovered devices.

Change-Id: Idd3d2949456a32c8c333744205755853aef80422
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>