Send notification when order is ready

[Ramin-RX7]

For now that this project is monolithic it's ok to have a notification system implemented within the project. However later on this needs to be sent to a celery task.

It's better to have an abstract class for notification system in case it grows into multiple types of notification (SMS, Email, Push notification, etc.)

• Notification when order is set (with an order id)
• Notification when order is ready
• Scheduled notifications for previous customers (based on specific statistics) (using celery)

[Ramin-RX7]

This task and the branch notification-system branch will be pended since the notification system is based on User model in the database which currently does not exist.

Once the #181 is completed (merged to develop branch), we will merge develop with notification-system and continue this task.