l10n: de.po: translate 260 new messages

Translate 260 new message came from git.pot updates in 9fa976f (l10n:
git.pot: v2.10.0 round 1 (248 new, 56 removed)) and 5bd166d (l10n:
git.pot: v2.10.0 round 2 (12 new, 44 removed)).

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

Author: ralfth