Refactor dynamic DNS updates
    
    Provides two new layers instead of the previous IPA specific layer:
     1) dp_dyndns.c -- a very generic dyndns layer on the DP level. Its
     purpose it to make it possible for any back end to use dynamic DNS
     updates.
     2) sdap_dyndns.c -- a wrapper around dp_dyndns.c that utilizes some
     LDAP-specific features like autodetecting the address from the LDAP
     connection.
    
    Also converts the dyndns code to new specific error codes.