Update for Moodle 5.0

[TamaroWalter]

🔀 Purpose of this PR:

• Fixes a bug
• Updates for a new Moodle version
• Adds a new feature of functionality
• Improves or enhances existing features
• Refactoring: restructures code for better performance or maintainability
• Testing: add missing or improve existing tests
• Miscellaneous: code cleaning (without functional changes), documentation, configuration, ...

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📝 Description:

This is the update PR for Moodle 5.0. The most important change in townsquare are the change for Bootstrap 5.0. Townsquare adapts to new classes of Bootstrap 5.0. This affects the UI of the sidepanel the most. As older Moodle version do not support the new Bootstrap classes, the a parallel sidepanel was kept for older Moodle versions.

The language strings of the side panel improved. In the course filter the full name of the course was replaced with the short name. This improves readability. For the letter filter, the names were changed to less technical ones.

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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 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

• Issue Improve template for mobile #12 is fixed with the new margin of the save/reset buttons and the bootstrap classes.

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

The new look of the side panel:

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