added helper for appending foreign DOM elements

Change-Id: I2af29313665f50fdfc8f654d19fe0a502cd8eb6b
Reviewed-on: http://gerrit.esdi-community.eu/3123
Tested-by: Jenkins <sitemple@igd.fraunhofer.de>
Reviewed-by: Simon Templer <simon.templer@igd.fraunhofer.de>