[Tails-l10n] (review) [de] various small edits

Hi,

I made some small edits across various *.de.po files and (tried to)
improve the wording here and there.

(The work is based on the testing branch, please tell me if that's wrong.)


Please review:

https://gitlab.com/flapflap/tails
branch: mostly-trivial
HEAD commit: aab64db8 - slightly twist/improve wording


Cheers,
~flapflap