Super-admin role account

**Is your feature request related to a problem? Please describe.**
The UI is missing account management with super-admin, admin and user roles.
When publicly exposed, anyone can create an account and use CompreFace without any validation nor management.

**Describe the solution you'd like**

**1. Account creation**
- Public account creation is only available for the first user, which will be promoted super-admin
- Once a super-admin is created and active, public account creation is disabled
- Only super-admins can manage accounts (creation, deletion)
- Upon creation, a private link will be generated for the newly created user to input his password

**2. User management**
- Super-admin can create apps and assign admin
- Admin can create services and assign standard user

[Strapi](https://docs.strapi.io/user-docs/getting-started/setting-up-admin-panel) is a good exemple of this process.

Thank you :)