Add support for viewing and refunding transactions

[aviupadhyayula]

Creates new viewset, serializer, and permission class to interact with transaction records. Superusers can see all transaction records. Non-privileged users must specify an event, and can only view transactions for that event if they're appropriately privileged.

Also contains minor modifications to attributes in TicketTransactionRecord.

TODO: still need to integrate with Cybersource's API for refunds.

Closes #756.

[codecov]

Codecov Report

❌ Patch coverage is 36.00000% with 48 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.68%. Comparing base (80bb21d) to head (52ca5c4).

Files with missing lines	Patch %	Lines
backend/clubs/permissions.py	24.00%	19 Missing ⚠️
backend/clubs/views.py	32.00%	17 Missing ⚠️
backend/clubs/models.py	33.33%	12 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           ticketing-v2     #768      +/-   ##
================================================
- Coverage         72.08%   71.68%   -0.40%     
================================================
  Files                32       32              
  Lines              6996     7068      +72     
================================================
+ Hits               5043     5067      +24     
- Misses             1953     2001      +48     

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[rohangpta]

Seems very valuable - is this a blocker to launch?

[aviupadhyayula]

OSA's expressed concern about the payments side of things in our conversations -- this isn't a blocker, but it's something that we want to have in place before our pilot. If we have to refund something, doing it through the Cybersource dashboard makes our internal accounting tricky.