* Event feedback functionality and related commits:
* blackness and isort and flake8 - this branch does not have pre-commit so I forgot :/
* finish backoffice management of eventfeedback
* add username to eventfeedback detail panel when viewed in backoffice
* Add feedback url to elm schedule. Fix access when user is anonymous. Remove print statement.
* one prefetch_related call to rule them all
Co-authored-by: Víðir Valberg Guðmundsson <valberg@orn.li>
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