Update noImagesLabel

[onmyway133]

In case of no images available on the phone, noImagesLabel displays in wrong position. So

• Update noImagesLabelbased on ImageGalleryView bounds, not collectionView.center. See http://stackoverflow.com/questions/29528643/why-do-layer-transforms-affect-a-uiviews-frame
• Animate noImagesLabel alpha change if user is about to drag down the ImageGalleryView

[RamonGilabert]

@onmyway133 🍣