Issue readonly

This pull request improves the returned message for hidden applications. Previously, the template took care of showing a message like: The application has not been found, while it should say that the user is not allowed to read the application.

For these reasons, the pull-request implements this feature in the require.app.read() method. If an application has been hidden, then, only the owner and the admins of the site can view it, otherwise you will get a 403 page.