Adds ability to use Apps in Navigation

Any App that has a `title` in it's `config.php` will be listed in Navigation.  Adding `no_nav` to the config will hide the App from Navigation even though it has a `title`.
Changed the 'if' statement to check value of 'no_nav'.
Changed the if statement to
if (array_key_exists ('include_in_nav', $ini) && $ini['include_in_nav']
            && array_key_exists ('title', $ini) && $ini['title'] != '') {
to make this off by default.
Fixed additional key_exists() call
Added include_in_nav in blog app