Added DuckDuckGo search engine support

DuckDuckGo search engine has been added as the last of the offered search engines for all
languages, and tools/get_search_engines.py has been patched so that it includes ddg in
answers eventhough it is not included in the chromium default search engine set.

Change-Id: I8b587587a17de891646842bfeba5ecd539a59e4c