RESPONDER: New interface for client registration This is just a beginning of new responder interface to data provider and it is just to make the client registration work. It needs further improvement. The idea is to take the existing interface and make it work better with further extensions of data provider. The current interface has several disadvantages such as it is originally build only for account requests and doesn't take different set of output parameters. It also doesn't work well with integration into tevent-made responders. Reviewed-by: Sumit Bose <sbose@redhat.com> Reviewed-by: Jakub Hrozek <jhrozek@redhat.com> Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>