Add Apps to Navigation


![Elefant CMS - Navigation](https://f.cloud.github.com/assets/3902182/320913/849ac628-9979-11e2-8406-41c12ea7a919.png)

I found the current way of adding Apps to the navigation menu using redirects in a web page rather odd.

This change adds the ability to add Apps to the menu by editing their `conf/config.php` file.  Any App with it's config file containing a non-empty `title` will be listed as a candidate for the navigation menu.  If you don't want an App shown in the menu even though it has a `title` then adding `no_nav = true` will hide it.