Move finding of scopes into scope manager

Maybe I'm barking up the wrong tree here, but let me know before I get too far down this path.

Basically we wanted to replace the Scope entity (so we can add extra field for referential integrity). We've already done it with the User and that was easy as you provide your own UserProvider and all is well. With scopes it wasn't so simple as the Client Manager and Scope storage both fetch scopes using the OAuth2ServerBundle:Scope repository. Meaning we'd have to extend/replace the scope storage and client manager if we wanted to use our own Scope entity.

All I've done here is have the Scope manager handle the two cases where you're fetching scopes. The manager service is passed into the Client Manager and the Scope storage.

I created a ScopeManagerInterface so anyone replacing the scope manager (like we wish to) can implement it to make sure they have the required methods.

This could also be done for Clients too.