AuthenticationEventPublisher Lookup

[jzheaux]

This PR addresses two main circumstances where Spring Security allows for an AuthenticationEventPublisher:

1. When published as a bean

@Bean 
public AuthenticationEventPublisher eventPublisher(ApplicationEventPublisher eventPublisher) {
    return new DefaultAuthenticationEventPublisher(eventPublisher);
}

2. When specified via the DSL

protected configure(AuthenticationManagerBuilder auth) {
    auth.authenticationEventPublisher(fooEventPublisher);
}