Структура NotificationEntity :
"_id" : ObjectId,
"userId" : ObjectId,
"tool" : object ({"type" : "editor"} | {"type" : "task", "taskId" : ObjectId}),
"type" : string (Если tool "task" ("owner" | "observer") если "editor" ("info" | "error" | "succes")),
"message" : string