Use time in notification data

Use custom time in notification data for change notification message on client

Example request:

{
  "to": "...",
  "data": {
    "title": "Ералаш",
    "body": "Начало в 16:30.",
    "icon": "https://eralash.ru.rsz.io/sites/all/themes/eralash_v5/logo.png?width=192&height=192",
    "click_action": "http://eralash.ru",
    "time": "1487003400",
  }
}