Added Html redirect support for RequiredRole

As per: http://stackoverflow.com/questions/17235947/requiredrole-razor2-and-html-redirect/17239023?noredirect=1#comment24979592_17239023

@mythz said he will modify it to look at Config.CustomHttpHandlers for any rules defined for HttpStatusCode.Forbidden
Added support for Html Redirect
Added support for Html Redirect
Added support for Html Redirect
Merge pull request #737 from discens/patch-1

Added HtmlRedirect support to RequiredPermision, RequiredRole, RequiresAnyPermission and RequiresAnyRole
Code tidy up from pull request #737.

Tidied up the code from pull request #737.  Removed duplicate code in
the 5 attributes that dealt with the HTML Redirects.
Merge pull request #738 from gregpakes/master

Cody tidy up from pull request #737.  Removed duplicate code and consolidated HTML Redirect logic within the base AuthenticateAttribute
Make RegistrationFeature AtRestPath user configurable
Update AuthProvider.cs

Enhancement per https://github.com/ServiceStack/ServiceStack/issues/741
Merge pull request #742 from CaspianCanuck/patch-1

Update AuthProvider.cs