Fix problem with leaving full screen mode.

All this commit does is explicitly run the logic of `resetFullScreen` on the EDT via `invokeLater`.

I did test things with `GuiUtils.invokeInSwingThread` and it seemed to work, but I opted for `invokeLater` because:

1. `GuiUtils.invokeInSwingThread` seems semantically equivalent to always using `SwingUtilities.invokeAndWait` ([and that shouldn’t be called from the EDT](http://docs.oracle.com/javase/7/docs/api/javax/swing/SwingUtilities.html#invokeAndWait%28java.lang.Runnable%29)).
2. Adding the runnable to the end of the EDTs queue—rather than executing the runnable immediately—seems like the safer choice, as there could be situations where events/threads reference the `fullScreenWindow` JFrame that has already been disposed of and nulled out.