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

Conflicts:
- .github/ISSUE_TEMPLATE/bug_report.md
  Took our version.
- CONTRIBUTING.md
  Updated the embedded copy of upstream's version.
- README.md
  Took our version.
- app/policies/status_policy.rb
  Not a real conflict, took code from both.
- app/views/layouts/embedded.html.haml
  Added upstream's changes (dns-prefetch) and fixed
  `%body.embed`
- app/views/settings/preferences/show.html.haml
  Reverted some of upstream changes, as we have a
  page dedicated for flavours and skins.
- config/initializers/content_security_policy.rb
  Kept our version of the CSP.
- config/initializers/doorkeeper.rb
  Not a real conflict, took code from both.

app/javascript/mastodon/locales/ja.json

@@ -15,7 +15,7 @@
   "account.follows.empty": "まだ誰もフォローしていません。",
   "account.follows_you": "フォローされています",
   "account.hide_reblogs": "@{name}さんからのブーストを非表示",
-  "account.link_verified_on": "Ownership of this link was checked on {date}",
+  "account.link_verified_on": "このリンクの所有権は{date}に確認されました",
   "account.media": "メディア",
   "account.mention": "@{name}さんにトゥート",
   "account.moved_to": "{name}さんは引っ越しました:",
@@ -95,10 +95,11 @@
   "confirmations.mute.message": "本当に{name}さんをミュートしますか？",
   "confirmations.redraft.confirm": "削除して下書きに戻す",
   "confirmations.redraft.message": "本当にこのトゥートを削除して下書きに戻しますか？ このトゥートへのお気に入り登録やブーストは失われ、返信は孤立することになります。",
-  "confirmations.reply.confirm": "返信",
-  "confirmations.reply.message": "今返信すると現在作成中のメッセージが上書きされます。本当に実行しますか？",
+  "confirmations.reply.confirm": "Reply",
+  "confirmations.reply.message": "Replying now will overwrite the message you are currently composing. Are you sure you want to proceed?",
   "confirmations.unfollow.confirm": "フォロー解除",
   "confirmations.unfollow.message": "本当に{name}さんのフォローを解除しますか？",
+  "conversation.last_message": "Last message:",
   "embed.instructions": "下記のコードをコピーしてウェブサイトに埋め込みます。",
   "embed.preview": "表示例:",
   "emoji_button.activity": "活動",
@@ -301,7 +302,7 @@
   "status.open": "詳細を表示",
   "status.pin": "プロフィールに固定表示",
   "status.pinned": "固定されたトゥート",
-  "status.read_more": "もっと見る",
+  "status.read_more": "Read more",
   "status.reblog": "ブースト",
   "status.reblog_private": "ブースト",
   "status.reblogged_by": "{name}さんがブースト",