de_DE small revision

I found some improper translations and also unitized the use of "Du"
instead of "Sie", which was inconsistent before.
Heisenberg Update & Revision

Translated the new strings, corrected some errors, and unitized the use
of "Du" instead of "Sie", which was inconsistent.
Merge German-translation update and recompile translations
Bump to 2.9.0~pre3