add cancel link

[The-Ludwig]

fixes #33

[codecov-commenter]

Codecov Report

Merging #177 (92d2982) into master (050a8d1) will decrease coverage by 0.04%.
The diff coverage is 76.00%.

@@            Coverage Diff             @@
##           master     #177      +/-   ##
==========================================
- Coverage   75.46%   75.43%   -0.04%     
==========================================
  Files          23       23              
  Lines        1011     1034      +23     
==========================================
+ Hits          763      780      +17     
- Misses        248      254       +6     

Impacted Files	Coverage Δ
member_database/events/__init__.py	63.11% <76.00%> (+1.12%)	⬆️

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[maxnoe]

Hi, we discussed this offline in the past (sorry, the issue was not updated).

Main points were that this is probably too complex to have the logic properly in the application and instead use human intervention for this part.

Some aspects that would need to be addressed:

• Simply cancelling should only be possible up to a certain date before an event

• Canceling should generate an email also to the event organizer

• If a person cancels and there is a waiting list, the next person on the waiting list should be contacted that there is a spot available again. What happens if that person does not respond? Responds that it cannot take the place? How much time do we give to respond? This requires a "cron-like" background task, something more complex web-apps regularly have, but which we did not yet need until now.

So to be honest, I think for the time being it is best to have canceling via a human performing the necessary actions (sending emails, using the admin interface to update the db)

[maxnoe]

see above...