HPC-9932: Add per-page backend page with a list of configured page elements, allowing to hide/unhide and remove, also add a discard changes button to the IPE links so that changes can be discarded without opening layout builder, which might fail if there are page elements present that run into memory issues

HPC-9932: Add per-page backend page with a list of configured page elements, allowing to hide/unhide and remove, also add a discard changes button to the IPE links so that changes can be discarded without opening layout builder, which might fail if there are page elements present that run into memory issues #851