[iOS] Only detects each image one time

[hohler]

Hello Miquido Team

I noticed that with multiple images, every image is only detected once.

Example: I have 2 images

1. recognize first image
2. recognize second image
3. try to recognize first image - it will not recognize it
4. recognize second image - works

I found a easy fix, maybe this is already the right way.

Replace

class ARQuidoViewController: UIViewController {
...
     if let nodeToRemove = detectedImageNode {
          nodeToRemove.removeFromParentNode()
     }
...
}

with

private var lastImageAnchor: ARImageAnchor?
...
class ARQuidoViewController: UIViewController {
...
       if let nodeToRemove = detectedImageNode {
            nodeToRemove.removeFromParentNode()
            if (lastImageAnchor != nil) {
                sceneView.session.remove(anchor: lastImageAnchor!)
            }
        }
...
}

[PiotrMitkowski]

Hello @hohler!

Looks good - would you mind creating a PR for it?