Make undoing a flight also undo the contracts attaching themselves to that flight.

Almost feel guilty about asking for this, I had a flight to do five contracts and a design feature I thought was working great was giving me fits.

So at the first launch the contracts attached themselves to that craft, I got to the bad patch and had to undo, fix it, relaunch. Got there and the contracts said "wrong craft", except some of them needed "start grounded" so I had to undo the flight again and reassign the contracts before launching.

Then I still couldn't get the damn autocircularizer to let go, so I had to do it again. Five more clicky-clicky-clicky sets to re-hang all the contract attachments to this flight.

This went on for an embarrassingly large number of flights, I was somewhat distracted, yeah, that's it.