Command pattern successful applied

The command pattern was successful applied in branch version_2.3.0_applyCmdPattern. All Tests are OK again. So I merged the branch version_2.3.0_applyCmdPattern into branch master.

Now I am working on branch version_2.3.0_addUndo to implement the undo/redo feature. You should find a new menu for this purpose.

Edit: I decided to add the menu items "Undo" and "Redo" below "Tools".