Code of conduct

What does this mr do?

• The mr adds the code of conduct as it was written in the linked issue.
• We display the coc to the users once every academic year. (the first time the users login in the new academic year)

In the current implementation it is not possible to force the students to see a new coc, in case we update it, if this is desirable this can be added later.

Screenshots

before

after

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made.
• Tests were created to test the feature.
• I have updated the documentation accordingly.
• I adhere to the style guide. closes #674