luci-app-ddns: Update to support ddns-scripts 2.1.0-3

* modified controller
     * remove support for ddns-scripts Version 1.x
     * ddns-scripts not correctly installed do not start
     * no config file create an empty one
* moved log settings to advanced tab
* set default syslog level "Notice"
+ removed special handling for dynamic_dns_helper.sh in postinst

Signed-off-by: Christian Schoenebeck <christian.schoenebeck@gmail.com>