Fixed de_DE.lang

Merged my grammatical corrections with Kobata's latest ones.

Some things I noticed:
- "\n" doesn't work, no line break, only the "/n" is added
- "Items" is not German
- "Item-Baum-Datei" was something that no one understood, "Stichwortverzeichnis" (keywords) fits much better
- "Auto-Auffüllen", "Auto-Ausrüsten" and "Auto-Sortierung" are shorter and all Germans should easily understand them with the tool-tips