Implemented prelimary icon support allowing UI widget to place image and model based icons on widgets


git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14389 16af8721-9629-0410-8352-f15c8da7e697
Fixed debug comment


git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14390 16af8721-9629-0410-8352-f15c8da7e697
Added preliminary icon to ComboBox.


git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14391 16af8721-9629-0410-8352-f15c8da7e697