German: Update translation

Patch set 1 - Translation for: Theme support & Dark theme
              http://review.cyanogenmod.org/#/c/26279/4
Patch set 2 - Fix derp. Add translation for dark theme
Patch set 3 - Changed and shortend wording
Patch set 4 - Minor fix to be in line with the other translations

Change-Id: I4f41c0589a06b6edf8000bc148ace1bd227f4083