[Security] Rename authentication_provider services to avoid name conflict

When using both anonymous and form authentication providers, they share the same service name whereas they use totally different classes.

Before : `security.authentication_provider.myfirewall`
After : `security.authentication_provider.myfirewall.dao` and `security.authentication_provider.myfirewall.anonymous`

The naming follows the recommendation for custom auth providers.
http://silex.sensiolabs.org/doc/providers/security.html#defining-a-custom-authentication-provider