Issue #23 Add Course and CourseProject classes Part 1

[SirJonithan]

This pull request implements the domain model classes for Course and CourseProject as well as a "ProjectMember" class which is imo necessary to work with Project memberships properly on a domain-level.
I wanted to integrate the structure first because i know other student's issues require the classes for their work.
For querying the related models i have not found to a good way to initialize these fields in a synchronous manner - would it be sufficient if provide asynchronous methods for fetching the related objects?
Also please let me know if it's in your interest to pursue the approach with the ProjectMember instances or if another approach would be superior.

[CLAassistant]

All committers have signed the CLA.

[joluj]

Thank you for you contribution! 2 small changes are required, but they both are a quick fix :)

Please make sure to use our pull request template. Usually the PR's description box should have been prefilled with this content. Was that not working?

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For querying the related models i have not found to a good way to initialize these fields in a synchronous manner - would it be sufficient if provide asynchronous methods for fetching the related objects?

I'm not sure if I understand the question correctly. Usually you fetch data from the DB and use that result to create the related object. Only the DB operation is asynchronous, the object creation and using the object can stay synchronous. Did I misunderstand something?

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Also please let me know if it's in your interest to pursue the approach with the ProjectMember instances or if another approach would be superior.

@dirkriehle Do you have a preference?

[SirJonithan]

Requested fixes were made, Changes are included in PR #62