we should be able to delete courses available for pickup from admin page

[fadyFH194]

Currently, it's only adding courses to the list but we can't remove them.
Admin should have control over adding and removing courses from that list

[RisticDjordje]

you can remove them wby using a negative number of courses. if the count is 0 it will be removed

[RisticDjordje]

this is a bit tedious but it works, it can be improved in the future with a direct remove course button.

[fadyFH194]

if a course available count is 0, it shouldn't appear on the list