I have a Macbook hooked up to an external monitor. I want to have a dual screen set up (currently just been using the external monitor by itself). However, I want the Macbok to ac as the second screen, and still use the monitor as the main screen. How do I do this? I can't seem to find a way in preferences. When it's in dual screen mode, and I click any application in the dock, it'll always open on my Macbook screen, and it's really annoying having to drag it across all the time. How do I make a new, say Safari window, open on my monitor?