Re-authorize participant without deleting

[blootsvoets]

Expected situation:
If a participant is marked as Authorized: false, a button is present to go through the authorization flow for that user again.

Current situation:
If a participant is no longer authorized, the only option to re-authorize now is to delete the entry.

Caveats:
There should be a message whether the new external user ID matches the old user ID once the authorization succeeds.