Introduce account document to user document

An account document is attached to a user document if an account of the
user is on the server. It may be missing if the user is on a remote server.

src/api/endpoints/posts/polls/vote.ts

@@ -100,7 +100,7 @@ module.exports = (params, user) => new Promise(async (res, rej) => {
 		});
 
 	// この投稿をWatchする
-	if (user.settings.auto_watch !== false) {
+	if (user.account.settings.auto_watch !== false) {
 		watch(user._id, post);
 	}
 });