Add setResolution method to ImageCapture QML type

On some devices the captured resolution can be really low and does not represent the capabilities of the camera used. 

With C++ API the issue can be worked around by calling the QImageCapture::setResolution(QSize) method when the QImageCapture::readyForCaptureChanged signal is received.

Making the same the same method available with the QML API would help to make the image capture work on all devices.