Change the names of GenericConfig and SecretConfig

[ajeklund]

As far as I can see, the GenericConfig class is intended and used only for strategy configuration objects, not all sorts of configuration objects (like SecretConfig). The GenericConfig name is hence a bit misleading, and I propose to change it to GenericStrategyConfig.

Also, it appears more natural and accurate to change the name of SecretConfig to AuthenticationConfig (since it configures an authentication process, not a secret process).