German translations improved and one Bugfix

With the first commit, I improved the german translation such that it is understandable without guessing.
Further, I corrected the " % s " bug which I mentioned in #65

I found a bug in the ConfirmPanel: When you modify the content of the text and click anywhere in the panel (e.g. change any other option), the modifications to the text were reverted. I applied an additional check to verify that it is only updated, when the "html" option is clicked.

Tested with Iceweasel 33.0 (yes, I managed to update it)