Introduce a basic user entity

[Yılmaz]

There are some libraries/modules exists to introduce a user-related backend like zfc-user but usually they are bloated, messy and far away from simplicity.

• Write a damn simple User entity (id, name, email, email_confirmed, password, reset_token). Anyone can easily improve later based on their requirements.
• Hash user passwords correctly.
• Create a data fixture for Users to populate database with few sample users.
• Document it.