de.pl: update German translations

de.pl: update German translations

This patch adds German translations for the new DNS CGI, some parts of
the hardware vulnerability mitigation CGI, improves some existing
translations and corrects some Deppenleerzeichen and Bildzeitungsbindestriche.

The third version of this patch is correctly based against upstream 'next',
honours Michaels opinion and contains updated language_issues.de and
language_missings files.

Since "./make lang" complains about missing translations marked as unused
in first place, no changes have been made to them in order to avoid
collateral damage.

Cc: Michael Tremer <michael.tremer@ipfire.org>
Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Acked-by: Michael Tremer <michael.tremer@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>