Improve UX for participants series overview
- Show chart which shows answer progress if there are answerable contents in this series
- Add labels to chart text
- Use half doughnut charts to save vertical space
- Remove svg image
- Add button to jump to next unanswered content
- Add hint if there are locked contents in this series
- Improve wording
Closes #1122 (closed)
Edited by Lukas Weingarten