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/locales/ja.json

@@ -170,7 +170,7 @@
   "navigation_bar.domain_blocks": "非表示にしたドメイン",
   "navigation_bar.edit_profile": "プロフィールを編集",
   "navigation_bar.favourites": "お気に入り",
-  "navigation_bar.filters": "Muted words",
+  "navigation_bar.filters": "フィルター設定",
   "navigation_bar.follow_requests": "フォローリクエスト",
   "navigation_bar.info": "このインスタンスについて",
   "navigation_bar.keyboard_shortcuts": "ホットキー",