Anonymize data when it's no longer needed

[jimbofreedman]

We should remove personally identifying information when we don't need it anymore:

• names
• contact details

We want to keep some things for statistics purposes:

• group makeup
• age
• post-code (coarse location)
• registration date/time
• match date/time

[alkemann]

Manual delete on the people tabs. Also ability to remove both participants from the match list is implemented