posts: add matrix-comments

add matrix commenting based on cactus

instead of using an appservice, we use a bot user to provision rooms for
us.

posts: kubeadm-psp: add whitelist for etcd path

js: remove gumshoe

sidebar: set author min-width

grid: always display excerpt

archive: truncate desc more on grid

grid: fix weird margin bottom

remove xl font size

grid: remake with css grid

enable lsi

date: fix forkawesome compatibility

use icons for pagination

move disqus noscript hint to the right space

light/dark: guard against missing disqus

light/dark: persistent config

reload disqus on light/dark change

css: dark/light: restrict to the container div

impl lightmode button

add yet another div for css hack selection