Better support for accompanying persons

[tomasr8]

Based on feedback from Science Gateway event coordinators

• Support for scanning QR codes for accompanying persons
• Make it possible to check in accompanying persons individually and independently from the main participant
• When scanning a QR code for accompanying persons show their name rather than main participant name
• Show accompanying persons in the list of all participants (probably nested in some way)

[ThiefMaster]

Make it possible to check in accompanying persons individually and independently from the main participant

I suggest implementing the part on the Indico side first since that goes into tickets (so the earlier this is available the better, since tickets generated between the 3.3 deployment and adding this extra data would not work for accompanying person checkins), and would be useful to have even before any support is present in the checkin app.

When scanning a QR code for accompanying persons show their name rather than main participant name

Showing both name in some way might be nice

[tomasr8]

Show accompanying persons in the list of all participants (probably nested in some way)

Note to myself, since we currently do not include registration data when fetching the list of registrations, we have no way to show the accompanying persons in the list. The data needed to do that is only loaded when the user navigates to a specific registration.

One solution would be to return the accompanying persons when fetching the list of registrations (while skipping other registration data)