Properly handle the case where QtWidgets is not available.

It does use a config test for now, just to make it clearer.  The Mac
backend currently requires widgets, but most of the others should work
without it (just not supporting QVideoWidget/WindowControl).

The QVideoDeviceControl interface was modified to remove the QIcon
usage - it was never implemented.

Unfortunately even the QML examples need widgets for the wrapper
application, and will need to be ported to QtGui based wrapper.

Change-Id: I8a55ad5cf09ab51749510bf16f49de0bd3f0bcdb
Reviewed-by: Ling Hu <ling.hu@nokia.com>

src/multimedia/controls/qvideodevicecontrol.cpp

@@ -105,13 +105,6 @@ QVideoDeviceControl::~QVideoDeviceControl()
     \since 1.0
 */
 
-/*!
-    \fn QVideoDeviceControl::deviceIcon(int index) const
-
-    Returns an icon for the video device at \a index.
-    \since 1.0
-*/
-
 /*!
     \fn QVideoDeviceControl::defaultDevice() const
 

src/multimedia/controls/qvideodevicecontrol.h

@@ -61,7 +61,6 @@ public:
 
     virtual QString deviceName(int index) const = 0;
     virtual QString deviceDescription(int index) const = 0;
-    virtual QIcon deviceIcon(int index) const = 0;
 
     virtual int defaultDevice() const = 0;
     virtual int selectedDevice() const = 0;