Fix interactive gallery dismiss going wrong direction when gesture starts out very slow

gallery's presenting VC from the view hierarchy

Closes #132

Tusker/Screens/Large Image/Transitions/LargeImageInteractionController.swift

@@ -29,7 +29,8 @@ class LargeImageInteractionController: UIPercentDrivenInteractiveTransition {
         var progress = translation.y / 200
         if let direction = direction {
             progress *= direction
-        } else {
+        } else if abs(progress) > 0.01 {
+            // if the progress is less than +/- 1%, don't set the direction because the translation may be random jitter in the user's finger
             direction = progress > 0 ? 1 : -1
             progress = abs(progress)
         }

Tusker/Screens/Large Image/Transitions/LargeImageShrinkAnimationController.swift

@@ -68,6 +68,12 @@ class LargeImageShrinkAnimationController: NSObject, UIViewControllerAnimatedTra
         blackView.backgroundColor = .black
         blackView.alpha = 1
         
+        // Save the old superview of toVC so we can move it back after the animation.
+        // It would be better to just not move toVC and instead remove from fromVC from the
+        // containerView so that toVC is visible behind it, but that doens't work for some reason
+        // (the entire screen just goes black, not even the contents of the containerView appear).
+        let oldSuperview = toVC.view.superview
+        
         containerView.addSubview(toVC.view)
         containerView.addSubview(blackView)
         containerView.addSubview(imageView)
@@ -88,6 +94,9 @@ class LargeImageShrinkAnimationController: NSObject, UIViewControllerAnimatedTra
             sourceView.alpha = 1
 
             transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
+            
+            // move the toVC back to the view that it was in before
+            oldSuperview?.addSubview(toVC.view)
         })
     }