I just installed Lightroom CC on my new laptop and the Undo button isn't showing up at the top right as it does on my old one (it's to the left of the Share button, separated by a vertical bar). I can't find a setting anywhere to show hidden toolbars. I can undo from the Edit menu or by pressing CTRL-Z, but I prefer the toolbar button. Any idea how to display the Undo/Redo toolbar?