(#15) Mention DuckDuckGo when sharing links on Twitter

When sharing a story, page or a search, display “via @duckduckgo for Android” instead of “via DuckDuckGo for Android” for any app that contains “twitter” in its package name.

Based on http://stackoverflow.com/a/8550043 and https://gist.github.com/mediavrog/5625602.