luci-app-ddns: Update to version 2.1.1-0

- adaption Makefile to changed luci.mk
- description in Makefile for correct version handling
- modified handling to detect and display installed version
- new functions ipkg_ver_installed() and ipkg_ver_compare
- correct wrong spellings
- modified language template and German translation

Signed-off-by: Christian Schoenebeck <christian.schoenebeck@gmail.com>