Support course overview, resolves #256.

[lucaboesch]

Note: Please fill out all relevant sections and remove irrelevant ones.

🔀 Purpose of this PR:

• [X ] Adds a new feature of functionality

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📝 Description:

Please describe the purpose of this PR in a few sentences.

• What feature or bug does it address?
• Why is this change or addition necessary?
• What is the expected behavior after the change?

See https://moodledev.io/docs/5.0/devupdate#activity-overview-page-integration

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📋 Checklist

Please confirm the following (check all that apply):

• I have phpunit and/or behat tests that cover my changes or additions.
• Code passes the code checker without errors and warnings.
• Code passes the moodle-ci/cd pipeline on all supported Moodle versions or the ones the plugin supports.
• Code does not have var_dump() or var_export or any other debugging statements (or commented out code) that
  should not appear on the productive branch.
• Code only uses language strings instead of hard-coded strings.
• If there are changes in the database: I updated/created the necessary upgrade steps in db/upgrade.php and
  updated the version.php.
• If there are changes in javascript: I build new .min files with the grunt amd command.
• If it is a Moodle update PR: I read the release notes, updated the version.php and the CHANGES.md.
  I ran all tests thoroughly checking for errors. I checked if bootstrap had any changes/deprecations that require
  changes in the plugins UI.

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🔍 Related Issues

• Related to Support course overview #256

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🧾📸🌐 Additional Information (like screenshots, documentation, links, etc.)

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[TamaroWalter]

Hi @lucaboesch,
thank you very much for adding the course overview in moodleoverflow too (I saw the contribution in ratingallocate few days ago)! 😁
I only adjust the new version number, as we only increase the date in the version if we support a new major moodle version :).
Have a nice weekend!