Fix the corner problem on collision

When the ball is going the same direction as the perpendicular we bounce
the right way. In addition I flipped the perpendiculars on the sides
which were incorrect and pointed inwards.

We now get some clipping on the corners, which could be removed by
rewinding the clock on update to make suere there is never a moment
where the ball overlaps the block - OR by making the ball travel faster
than the paddle.