Add structure level in participant export

[Elblinator]

Currently:
When you export a participant list then the structure level are not exported

Reproduction:

1. navigate to participant-list
2. add some structure levels to some participants
3. export the participant-list
4. the structure levels are not exported

Wanted:
The structure levels should be exported

[reiterl]

I have looked at this. Updating the import will fix this too, if done correct. So waiting on the import to include the structure_levels.