* gl/inc/TGLViewer.h:
	* gl/src/TGLViewer.cxx:
	Added customizations of update/redraw behaviour:
	1) flag 'Bool_t fIgnoreSizesOnUpdate' that tells the viewer
	   not to check the size of the object in AddObject();
	2) member 'Color_t fClearColor' that allows user to select the
	   background color;
	3) method 'void UpdateScene()' thet forces the scene update via
	calling 'fPad->Paint()';
	4) method 'virtual void RefreshPadEditor(TObject* changed=0)' that
	   allows updates to be sent to the built-in editor when the
	   internal state changes.

	* gl/inc/TGLSAViewer.h:
	* gl/src/TGLSAViewer.cxx:
	Implemented virtual 'TGLSAViewer::RefreshPadEditor()'. In all
	calls to 'TGedEditor::SetModel()' replaced third argument 'Int_t
	event' from 'kButton1' to 'kButton1Down'.

	* gl/inc/TGLViewerEditor.h:
	* gl/src/TGLViewerEditor.cxx:
	Added widgets controlling 'fClearColor', 'fIgnoreSizesOnUpdate',
	'fResetCamerasOnUpdate' and 'fResetCameraOnDoubleClick'; added
	buttons for invoking 'UpdateScene()' and 'CameraHome()' methods.

	* gl/src/TGLScene.cxx:
	Removed code setting the glClearColor in 'Draw()'.


git-svn-id: http://root.cern.ch/svn/root/trunk@16452 27541ba8-7e3a-0410-8455-c3a389f83636