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/packs/public.js

@@ -1,5 +1,8 @@
 import loadPolyfills from '../mastodon/load_polyfills';
 import ready from '../mastodon/ready';
+import { start } from '../mastodon/common';
+
+start();
 
 function main() {
   const IntlRelativeFormat = require('intl-relativeformat').default;