Background: In Piwik 2.13 we removed the `Site.setSite` event because it is slow. So in some cases it may not actually trigger a `Sites.setSites` event when a site is loaded. For example when doing `new Site()`. I think in this case we should still trigger that event if the site did not exist yet because we do not call it very often and not in a loop for all sites etc. This is useful since `new Site` is used eg in `Controller` and for such cases we should trigger this event.