Add Apps to Navigation


![Elefant CMS - Navigation](https://f.cloud.github.com/assets/3902182/320818/fc05588a-996b-11e2-839a-c905d606a5c2.png)
Allows Elefant Apps to be added to the Navigation.  It simply adds all Apps that have a `title` (but no `no_nav` key) in their `conf.php` to the list of selectable items.

To me, the current way of adding Apps to the Navigation using redirects seems a bit odd as the navigation URL will be different from the actual URL.