Fixes example for view customization docs

The code example in https://github.com/jaliss/securesocial/blob/master/docs/src/manual/source/guide/views-customization.md contains bugs. It looks like people have been running into issues with this for months.

* Type for application should be play.Application 
* Should be views.html.custom not view.custom.html
* getNotAuthorizedMethod should be implemented otherwise it throws errors