Removed link option and updated German translation.

I've removed the "Include link to YouTube" option in my branch. It is kinda redundant as YouTube offers a button in its player that does exactly the same, with the benefit of pausing the current video and resuming it on their page where you left off. Devices withouth Flash should not be a concern as YouTube offers a HTML5 player. Plus it is not even working at the moment. editor.insertElement only inserts the first element (the video) and discards the appended link tag. Could be fixed by wrapping everything into a &lt;div&gt; or so, but oh well ...

I've also updated the German language file:
* I changed chkPrivacy to the wording YouTube uses in their embed options.
* chkRelated sounded a bit weird.
* txtResponsive was not translated yet.