Fixed VFW video capture

Implemented missing CvCaptureCAM_VFW::setProperty() member function (handling CV_CAP_PROP_FRAME_WIDTH, CV_CAP_PROP_FRAME_HEIGHT, CV_CAP_PROP_FPS properties).
Extended CvCaptureCAM_VFW::setProperty()/getProperty() functions (can handle CV_CAP_PROP_FPS property).
Minor refactoring of CvCaptureCAM_VFW class.
(These are the same changes which were already applied in 2.4 branch - see PR 2640).