Updates for Qubes 4.0.1

[redshiftzero]

Qubes 4.0.1 includes Whonix 14 and Fedora 29, so we should:

• Run through workstation provisioning on Qubes 4.0.1 and update the README to indicate we should install on Qubes 4.0.1
• Handle removal of jessie-backports repo - Debian9 template: outdated repositories (/etc/apt/sources.list). [easy fix?] QubesOS/qubes-issues#4917
• Update test_all_fedora_vms_uptodate here to point to fedora 29
• Remove section in docs instructing users to remove EOL whonix templates: https://github.com/freedomofpress/securedrop-workstation#upgrading-sys-whonix-and-whonix-ws-appvms-to-whonix-14
• Remove section in docs instructing users to upgrade to Fedora 28: https://github.com/freedomofpress/securedrop-workstation#upgrading-sys-net-sys-usb-and-sys-firewall-to-fedora-28

[redshiftzero]

Once this issue is completed, #191 and #189 can be closed

[conorsch]

WIP branch at https://github.com/freedomofpress/securedrop-workstation/tree/245-first-run-for-qubes-4.0.1

There's one remaining problem: the quiet=true param doesn't seem to be working, which is causing the jessie-backports cleanup to fail on specifically the Whonix VMs. We can probably make that conditional without use of the quiet param. Will circle back and take another look.