[Demo] Enhance and fix up the setup experience in prepare-dev.py.

Review Request #11392 — Created Jan. 21, 2021 and discarded — Latest diff uploaded

Information

Review Board
release-4.0.x

Reviewers

This modernizes the way we request input and display output on
prepare-dev.ppy, utilizing more of rb-site's ConsoleUI. This is a
better, more consistent way of displaying information and prompting for
information.

The text has been updated to be more user-friendly, to offer
guidance for when things go wrong, and to provide next steps when the
environment is prepared.

Tested prepare-dev.py.