fix: DELETE periods throws 404 even if the entity exists

[linear[bot]]

KIR-61 fix: DELETE periods throws 404

[Tschonti]

I couldn't reproduce this. But sometimes the deleted period doesn't disappear from the period list until the page is refreshed

[mozsarmate]

I get a 404 each time if the period has at least one applicaiton assigned to it. I succed to delete the period after i delete all the applications assigned manually

[mozsarmate]

maybe we should implement a delete applicaiton button for the admins?? @FearsomeRover

[Tschonti]

or you need to set the onDelete to cascade on the applicationPeriod entity so deleting it will delete all the related applications as well