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/mastodon/initial_state.js

@@ -13,5 +13,6 @@ export const me = getMeta('me');
 export const searchEnabled = getMeta('search_enabled');
 export const maxChars = getMeta('max_toot_chars') || 500;
 export const invitesEnabled = getMeta('invites_enabled');
+export const version = getMeta('version');
 
 export default initialState;