[Tails-l10n] (review)[de] Installation assistant: expert

Hi,
I translated the expert section of the installation assistant. It
contains following files:
wiki/src/install/expert/usb.de.po
wiki/src/install/expert/usb/overview.de.po
wiki/src/install/inc/steps/install_tails_installer.inline.de

Please review:

https://gitlab.com/spriver/tails.git
branch: de_install_expert
HEAD commit: 18ed28f Initial translation

Cheers!
spriver