Move delete button for backlog items for consistency
Add loading overlay to movies that are added optimistically so further actions aren't performed
Ensure delete/add functions are performed sequentially to avoid race condition on the backend (correct solution would be database transactions. I've logged #169 to be actioned in the future)
Ensure lists can only be edited by users in club (whoops, I can't believe I forgot to include this in the lists PR)
Changes: