This is a photo app copy cat demoing how to use PhotoKit.

• Check for Photo Library Authorization
• Fetch AssetCollections and PHAssets from PHPhotoLibrary
• Listen for PHPhotoLibrary changes
• Image Caching
• Display thumbnail images for assets fetched
• Display the Asset itself we have fetched. That is images, videos, and etc. 
• Create new PHAssets from Data, AVAssets and save it to PhotoLibrary.
• Delete PHAssets
• Modify PHAsset property
• Modify PHAsset content