Split modules types in Identity and Authenticator
    
    The same module may implement both types, but initializatrion will be
    nonetheless performed separately, once for the identity module and once for the
    authenticator module.
    
    Also change the proxy module to retireve the pam target name from the domain
    configuration so that it is possibile to create per-domain pam stacks.
    
    With this modification it is actually possibile to use normal nss and pam
    modules to perform a successful authentication (tested only with sudo so far)
    
    Update exmples.