Convert DomainBase's contacts to VKeys (#574)

* Convert DomainBase's contacts to VKeys

Convert usage of DomainBase contacts from Key to VKey.  This is the same
change as done for nameserver hosts, as it affects all external interfaces.
As with nameserver hosts, we preserve the existing representation so as not to
afffect the datastore representation.

db/src/main/resources/sql/schema/db-schema.sql.generated

@@ -100,8 +100,10 @@
         last_epp_update_client_id text,
         last_epp_update_time timestamptz,
         statuses text[],
+        admin_contact text,
         auth_info_repo_id text,
         auth_info_value text,
+        billing_contact text,
         fully_qualified_domain_name text,
         idn_table_name text,
         last_transfer_time timestamptz,
@@ -109,9 +111,11 @@
         launch_notice_expiration_time timestamptz,
         launch_notice_tcn_id text,
         launch_notice_validator_id text,
+        registrant_contact text,
         registration_expiration_time timestamptz,
         smd_id text,
         subordinate_hosts text[],
+        tech_contact text,
         tld text,
         primary key (repo_id)
     );