public string AddLink(string url, string source, string sourceElement)
{
url = UrlHelper.MakeAbsolute(source ?? baseUrl, url);
string id = UrlHelper.Standardize(url);
SiteItem item = state.GetOrAdd(id, new SiteItem(id, baseUrl, url, source, sourceElement));
ItemAdded.Trigger(this, new ItemAddedEventArgs(item.ID));
return(item.ID);
}