Complete DTA plugin improvements

See merge request !3

- Added externallib.php with save_submission web service
- Added callback.php for backend result callbacks
- Added db/services.php for service definitions
- Fixed property names in dta_result and dta_result_summary
- Added .gitignore for temp files
- Added CHANGELOG.md documenting v2.1.0 changes
- Plugin tested successfully with CI/CD pipelines

- Fixed file include path (DtaResult.php -> dta_result.php)
- Replaced magnifying glass with 'More Details' button
- Added colored test result labels (green/yellow/red)
- Improved button styling to match Grade button
- Fixed cmid parameter handling for view.php
- Translated German comments to English
- Hide competencies with 0% values
- Enhanced UI/UX with proper alignment and hover effects

plagarism data removed + provider bugs fixes and delete data functionality.

See merge request !2

Coding style and recommendations

See merge request !1