Implement logout user funtionality

[R055A]

Description

Implemented functionality for logging out a user by HTTP POST request.

The user is first verified as logged in and then the authorization token is set to "0" in the user database document.

Related Issue

Solves #19

Type of change

• New feature (enhancement)

How Has This Been Tested?

Automated testing for successful logging out a user, and unsuccessfully logging out a user with invalid ID and invalid authorization token.

• Automated testing

Checklist:

• Does a similar (open or closed) pull request not already exist?
• Is the pull request head repository a fork repository?
• Is the pull request compare branch a development branch?
• Is the code documented, particularly in hard-to-understand areas?
• Does the code build without new warnings?
• Has testing been performed that proves changes are effective and work?
• Has a self- and/or peer-review of the code been performed?
• Does all new and existing automated testing pass?
• Is the person responsible for the repository assigned to the pull request?
• Is the pull request linked to a project?
• Is the pull request linked to a milestone?

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