Bugfix exam form

[tobias-wiese]

Reason for this PR

• Date object was parsed in a wrong way
• resetting course and module did not work on failure
• exam list crashed when student fetched exams but no matching courses

Changes in this PR

• fix parsing of object
• watching the viewMode prop to react on page navigation
• setting course and module explicitly in basics-section
• only fetch exams if the courses were found

Type of change (remove all that don't apply)

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Manually tested all use cases this could alter

Checklist: (remove all that don't apply)

• I have performed a self-review of my own code
• My changes generate no new linting warnings or console warnings
• I have updated the CHANGELOG.md to include any changes made in this PR (add WIP to the top, if there is none already)