Merge branch 'master' into glitch-soc/merge-upstream

Conflicts:
	Dockerfile
	app/javascript/packs/common.js
	config/webpack/loaders/sass.js
	config/webpack/shared.js
	db/schema.rb
	package.json
	yarn.lock

A lot of the conflicts come from updating webpack.

Even though upstream deleted app/javascript/packs/common.js, I kept
glitch-soc's version as it unifies JS/CSS packs behavior across flavours.

Ported glitch changes to webpack 4.x

app/javascript/core/admin.js

@@ -1,6 +1,9 @@
 //  This file will be loaded on admin pages, regardless of theme.
 
 import { delegate } from 'rails-ujs';
+import { start } from '../mastodon/common';
+
+start();
 
 function handleDeleteStatus(event) {
   const [data] = event.detail;