Refactored basic error presentation into a category on NSResponder.

I was still occasionally getting errors that were presented from a background queue, which is bad. This should make sure that that doesn’t happen anymore.
Fixed a small bug in the display of the status view.

If the window controller encountered an error during processing, the status view remaining on-screen. This put its “toggle” state in the opposite state as the actual local preview, but preserved all of its connected actions. Hilarity ensued.