Allow custom persistence managers

[frankdekker]

Added support for configuring custom persistence manager.
As improvement implementation on #145

Configuration:

league_oauth2_server:
    persistence:
        custom:
            access_token_manager: App\Manager\MyAccessTokenManager
            authorization_code_manager: App\Manager\MyAuthorizationCodeManager
            client_manager: App\Manager\MyClientManager
            refresh_token_manager: App\Manager\MyRefreshTokenManager
            credentials_revoker: App\Service\MyCredentialsRevoker

Code changes:

• Extended the Configuration class.
• Added support in the Extension class.
• Skipped the doctrine extension check if in_memory or custom persistence is chosen.
• Added acceptance test, testing the different auth flows.
• Updated the readme.md to include instructions how to set the custom persistence managers.

Implementation notes
I would've really liked to make doctrine/orm not a mandatory dependency but move it to the suggests section in composer.json. We have a project where we can't use Doctrine, and need to implement our own persistence manager, but now 6-7 doctrine packages will be included in the project. Could we move doctrine/orm to suggests section in a future version?

[Nattfarinn]

You probably will have to add support for https://github.com/thephpleague/oauth2-server-bundle/blob/master/src/Service/CredentialsRevokerInterface.php as its implementation also relies on ORM ("been there, done that"). I like your approach more, even if is a bit more invasive.

[frankdekker]

You probably will have to add support for https://github.com/thephpleague/oauth2-server-bundle/blob/master/src/Service/CredentialsRevokerInterface.php as its implementation also relies on ORM ("been there, done that"). I like your approach more, even if is a bit more invasive.

Thanks, i've added support for the credentials revoker :).

[chalasr]

It took time, but here we go, this is in now. Thank you very much @frankdekker.