Add properties to swift extensions

add-properties-swift-extensions.swift

    typealias IMG_VIEW_REQUESTS_TYPE = [ UIImageView : [String] ]

    private struct AssociatedKey {
        static var imgViewRequests = "imageCache_imgViewRequests"
    }
    
    var imgViewRequests : IMG_VIEW_REQUESTS_TYPE {
        get {
            return objc_getAssociatedObject(self, &AssociatedKey.imgViewRequests) as! SmartSingleton.IMG_VIEW_REQUESTS_TYPE
        }
        set(downloader) {
            objc_setAssociatedObject(self, &AssociatedKey.imgViewRequests, downloader, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }