Create a user model

[Kiblindh]

Description

We need to create a user model that contains several relevant fields such as
*user_type (admin, interviewer or applicant)
*date_created
*first_name
*last_name
*email
*password
*hasApplication = boolean field that tells if the user has applied
=>Only relevant for the users of applicant type

Proposed solution

Create a schema that contains the fields using mongoose.schema function