Updated German language file

Last minute minor fix ("dem Mod" to "der Mod") to my updated file some minutes ago:

Fixed almost all German lines. There are still no translation lines for shortcuts help (the tooltip "Shortcuts help", the red text "WARNING: Since 1.3.1, shortcuts won't work ..." and the button "Done".

I think I worked on the old translation as well, in the beta times. I'm not sure anymore, but it feels so. Anyway, now it's far better than before!