FluxBB replacement

FluxBB isn't maintained so we need to migrate to something else.

https://lists.archlinux.org/pipermail/arch-devops/2019-October/000297.html

The below feedback has been solicited from the current Arch Linux Forum
team in October 2019, based on the premise that the DevOps team desires to
replace the current forum software.

The points have been summarized for readability, and anonymized to ensure
the points are considered based on their merit alone.

Our preference is that a demo system is set up prior to a final decision
being made so we can evaluate the moderation tools available to assess
their suitability for our community behaviors.

General Criteria
===============
  *  I hope that we will stick to simple and not deviate too far from the
functionality of a basic forum.
  *  I would opt for disabling all unnecessary features
  *  I am very skeptical of any system of community voting for relevance.
  *  The forum should remain a technical resource and not devolve into
karma farming.
  *  I would also strongly oppose any sort of obligatory 2-factor
authentication.
  *  Reasonably good functionality on limited bandwidth and/or text-mode
browsers.
  *  I would like better tools to help identify duplicate accounts
  *  Perhaps tools that can auto-detect behavior such as post blanking when
it starts.
  *  I'm not a fan of endless scrolling or javascript "features" either,
and I don't see any point of social media things like "likes" on a
technical support forum.
  *  KISS.
  *  One of the things that I hate most in the world is continuous scroll
down rather than pagination.
  *  Functionally, FluxBB does everything I expect a forum software to do.
  *  It shouldn't contain post-voting facilities
  *  I dislike sub-threading where one can reply to other posts inline. If
reddit is any indication it leads to incredibly messy and hard to follow
discussions.
  *  I liked myBB and misago the most from some quick browsing through the
examples.
  *  Based on several criteria above, Discourse seems like a particularly
poor fit for our community.
  *  "Oh dear god, anything but discourse."

Alternatives
===============
phpBB
  *  https://www.phpbb.com/
  *  Seems still actively developed.
  *  Is listed on some "top 10" forum software for 2019 sites.
  *  It is very similar to fluxBB.

Thredded
  *  https://thredded.org/
  *  It is actively developed
  *  Free & open-source
  *  Has a 'modern' visual style (while being readily
customizable/themeable)
    Can be used with a SSO
    Paginates
    Demos I've found load quickly and are easy to read on a TUI.

MyBB
  *  https://mybb.com/
  *  Maintained
  *  Has an LDAP plugin.

Farum
  *  https://flarum.org/features/
  *  Seems to be similar to discourse; claims to be lightweight.
  *  Has SSO, API, and Anti-spam.
  *  Still beta release.

Vanilla
  *  https://open.vanillaforums.com/
  *  Maintained
  *  Open-core/Freemium model.
  *  Has SSO.

Misago
  *  https://misago-project.org/
  *  "Looks OK from a bit of playing around on their site. Not sure what
moderation tools look like."

Discourse
  *  https://www.discourse.org/
  *  There seems to be a lot of bells and whistles that increase its
complexity but I have no experience with it.
  *  Discourse ... design philosophy seems to be in the mindset of catering
to the majority who have high powered systems, good network connections,
and "modern" (GUI) browsers. The Arch community has always seemed to work
hard to not needlessly marginalize those who have limited bandwidth, old
hardware, or text-mode browsers; so the use of a tool like discourse
strikes me as either antithetical to our existing community ethos, or a
sign of a significant change in direction.