Save the olm account after we create new one-time keys

Otherwise after a restart the old account will be loaded and we
won't be able to decrypt messages from devices using the new one-time keys.

Also new one-time key upload requests will fail due to conflicts with
the existing keys with the same keyid.

include/Olm.hpp

@@ -75,4 +75,7 @@ encrypt_group_message(const std::string &room_id,
                       const std::string &device_id,
                       const std::string &body);
 
+void
+mark_keys_as_published();
+
 } // namespace olm