Replace screen in Overflow with another without having to redo connectors#56

Sometimes one needs to add a new screen into a flow from Sketch that is completely different and/or has a different name from the one in Overflow.

At the moment, you have to import the new screen, remove the old one, and then re-instate all the connectors and everything.

It would be great if there was a way to replace a screen in a flow with another and retain the properties / connection of the old screen.