Improve participants question series overview
The question series overview has been removed from the stepper. Instead the view is shown standalone when navigating into series if:
- series contains slides and/or flashcards only
- one or more questions already has been answered
- last content has been answered
According to this adjust series overview component to handle different answer states:
- Pure info series (slides and flashcards only)
- Partially answered series
- Fully answered series
Furthermore allow navigating to series overview if content has answered. So no longer all contents must be answered to be able to see the overview.
Closes #981 (closed), #968 (closed), #897 (closed)