l10n: de.po: update German translation

Translate 96 new messages came from git.pot update in dfc182b (l10n:
git.pot: v2.13.0 round 1 (96 new, 37 removed)).

Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>
Acked-by: Matthias Rüster <matthias.ruester@gmail.com>

Author: ralfth