Add server-side checks for exercise imports - Fixing #305
The main contribution of this merge request is the integration of additional server-side checks during the import of exercises from Artemis.
Other changes included here:
- Refactoring of the
ExerciseImportService
- Integration of PMD and Sonarlint code smells
- Simple sanitization of the user provided metadata (replacement of literal characters '<' and '>' with its corresponding HTML '<' and '>')
- Restored and increased coverage for client-side tests (
exercise-import component
)