Port Tails Installer to Python 3

Liveusb-creator should be migrated to python3.

Feature Branch: https://gitlab.com/saschamarkus/liveusb-creator/tree/feature/10085-Port-Tails-Installer-To-Python3

Parent Task: #5958

Related issues

Related to #7036

Original created by @alant on 10085 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information