Seed using model add delay to requests

[Reinoptland]

What this pullrequest does:

Changes seeds:

• Seed users using a sequelize model
• Seed users using .upsert to validation errors cause by unique emails

Adds a delay middleware:

• Implement a delay middleware that delays each request 1000 ms
• This is to better simulate the time normal network traffic would take
• Allows students to practice showing loading spinners and so on