Updated german translation

This is an Update of the german Translation. This should now be fairly
complete.

I adjusted some of the translations. Main point of the adjustment is the
switch from the formal "Sie" to the informal "du".

Feedback welcome!
You should probably put the closing bracket for the </strong> tag back :-)
Everything else looks good. Thanks :-) (Oder mal wie ich es gewohnt bin: Dankö)