Bugfix: prevent player shooting + movement while dead, add self destruct option (F1) to unstick player

After a few comments on the silliness of being able to shoot whilst dead, I've decided to fix the issue by whacking the below on the shooting / movement code:

if (gameObject.layer.Equals(Constants.Layers.DeadThings))

{

  return;

}

Also added self destruct option (F1) to unstick player - there is no cost to this, you will be returned to the previous check point in the level.