added login event to firewall listener (like security.interactive_login)

I'm using the OAuthServerBundle with the Password grant to directly login users from a frontend into a backend accessible through an API. 
In the backend I normally set a lastLoginDate through the security.interactive_login event. This event is not thrown when logging in through the OAuth firewall.

I implemented a simple OAuthLogin event that is thrown when a user logs in through the OAuth firewall. The event just contains the token with the authenticated user.

Please comment if there's a better or more general way to do it. If the implementation is right, I'll also submit an appropriate test. Thanks.