//This method allows users to query for more messages by dragging down from the top.
func scrollViewDidScroll(_ scrollView: UIScrollView){
    //If we are not loading more messages already
    if(!loadingMore){

        //-40 is when you have dragged down from the top of all the messages
        if(scrollView.contentOffset.y < -40 ) {
            loadingMore = true
            addHistory(start: earliestMessageTime, end: nil, limit: 10)
        }
    }

}