Updated LoginController template to include an import of SpringSecurityS...

In grails-2.3.0.RC1, LoginController template fails with an error (as seen in the image below) "Cannot call isLoggedIn on null object." I fixed this by explicitly importing SpringSecurityService. 

PS: Also to let you know, the "@Secured(...)" annotation needs to be explicitly imported for it to work with grails 2.3, if you would like to update the tutorials section of the documentation to include this.

![screen shot 2013-08-21 at 2 10 25 pm](https://f.cloud.github.com/assets/340027/1003408/09770a94-0a8d-11e3-84eb-8f4c74366d9e.png)