Improve notification (#8835)

* Improve notifications

* batch load user

* Update notification only when read

* Fix reorder

* fix lint

* fix test

* fix lint

* make function meaningful

* fix comment

models/migrations/v108.go

@@ -0,0 +1,18 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package migrations
+
+import (
+	"xorm.io/xorm"
+)
+
+func addCommentIDOnNotification(x *xorm.Engine) error {
+	type Notification struct {
+		ID        int64 `xorm:"pk autoincr"`
+		CommentID int64
+	}
+
+	return x.Sync2(new(Notification))
+}