Added osgGA::Device class for integration of both physical and virtual devices.

Added template readFile(..) function to make it more convinient to cast to a specific object type.

Added support for osgGA::Device to osgViewer.

Added sdl plugin to provides very basic joystick osgGA::Device integration.

include/osgViewer/ViewerBase

@@ -117,7 +117,6 @@ class OSGVIEWER_EXPORT ViewerBase : public virtual osg::Object
         osg::BarrierOperation::PreBlockOp getEndBarrierOperation() const { return _endBarrierOperation; }
 
 
-
         /** Set the done flag to signal the viewer's work is done and should exit the frame loop.*/
         void setDone(bool done) { _done = done; }