Feature: user authentication

[runabol]

This PR adds support for user creation and user assignment when a job is created.

1. New users table to store username and passwords (hashed).
2. A new built-in guest user that can be assigned to jobs when login is not enforced.
3. New endpoint to create users: POST /users.
4. createdBy field added to each job.

To turn on login using basic auth use middleware.web.basicauth=true or TORK_MIDDLEWARE_WEB_BASICAUTH_ENABLED=true