Update german strings.xml

* typos fixed
* small changes
* untranslated translation added

Update:
I added a new version here [download](http://pastebin.com/download.php?i=zHnkXPPm), I hope it fix all problems. [Raw](http://pastebin.com/raw.php?i=zHnkXPPm) version.

Btw:
Congrats on release 1.0! :+1: