add archmanweb role

@eschwartz kindly moved mandoc into [community], so now we can test the whole role and discuss how it should be deployed.

I'm testing the role in a systemd-nspawn container with this playbook. The roles (except mkcert as a replacement for certbot) are taken directly from the Arch infrastructure repo, so it should match the production environment close enough.

I still have some (mostly small) things on my list:

• discuss the release model we want to follow
• figure out verification of GPG signatures with Ansible (split into #266)
• reorganize site settings for production and development (this should be improved on the project side)
• do more extensive testing of the update script
• update the links and text on the front page
• improve the navbar, figure out how to use archlinux-common-style directly

In the container it currently looks like this:

Some random ideas for when it is deployed:

• adding a "Manpages" or "Man" link to the main navbar on other Arch sites: I think the best way forward is to make the current navbar responsive and depending on how it turns out, we can discuss if adding more links (potentially also Gitlab, reproducible.archlinux.org) or other reorganization is feasible
• @jelle's idea: add a "Man pages" link to the "Package Actions" in the archweb's package detail view (pull request)
• @svenstaro's: mobile experience should be improved (e.g. responsive navbar is needed)