visualgst: Refactor some Smalltalk undo commands

Make them subclass of Command. Smalltalk commands don't works as undoable
commands, they could only be executed: a simple eval in the workspace could
break the undo/redo code.

2013-06-17  Gwenael Casaccio  <gwenael.casaccio@gmail.com>

        * Commands/System/AddClassCommand.st: New system command
        * Commands/System/AddMethodCommand.st: New system command
        * Commands/System/AddNamespaceCommand.st: New system command
        * Commands/System/DeleteClassCommand.st: New system command
        * Commands/System/DeleteMethodCommand.st: New system command
        * Commands/System/DeleteNamespaceCommand.st: New system command
        * Commands/System/RenameCategoryCommand.st: New system command
        * Commands/System/RenameClassCommand.st: New system command
        * Commands/System/RenameNamespaceCommand.st: New system command
        * Commands/CategoryMenus/RenameCategoryCommand.st: Updated to new system command
        * Commands/ClassMenus/AddClassCommand.st: Updated to new system command
        * Commands/ClassMenus/DeleteClassCommand.st: Updated to new system command
        * Commands/ClassMenus/RenameClassCommand.st: Updated to new system command
        * Commands/Command.st: Updated to new system command
        * Commands/MethodMenus/DeleteMethodCommand.st: Updated to new system command
        * Commands/NamespaceMenus/AddNamespaceCommand.st: Updated to new system command
        * Commands/NamespaceMenus/DeleteNamespaceCommand.st: Updated to new system command
        * Commands/NamespaceMenus/RenameNamespaceCommand.st: Updated to new system command
        * Commands/SmalltalkMenus/AcceptItCommand.st: Updated to new system command
        * Undo/AddClassUndoCommand.st: Deleted
        * Undo/AddMethodUndoCommand.st: Deleted
        * Undo/AddNamespaceUndoCommand.st: Deleted
        * Undo/DeleteClassUndoCommand.st: Deleted
        * Undo/DeleteMethodUndoCommand.st: Deleted
        * Undo/DeleteNamespaceUndoCommand.st: Deleted
        * Undo/RenameCategoryUndoCommand.st: Deleted
        * Undo/RenameClassUndoCommand.st: Deleted
        * Undo/RenameNamespaceUndoCommand.st: Deleted
        * package.xml: Update