Add getAvailableDevices into Core interface

[huningxin]

It maps to Core::GetAvailableDevices. The JS API sketch could be

partial interface Core {
  sequence<DOMString> getAvailableDevices();
};

[lionkunonly]

@dkurt Hi, dkurt. Do you know why the log [E:] [BSL] found 0 ioexpander device is printed when I use Core::GetAvailableDevices on my computer?

[dkurt]

Hi! We also observe it in OpenCV. Not sure if it is a bug inside Inference Engine or not.