Method unbind

src/timeline/src/item.cpp:1399–1404

make copty safe.. ICK

// make copty safe.. ICK
void Item::unbind() {
    item_pre_event_callback_  = nullptr;
    item_post_event_callback_ = nullptr;
    for (auto &i : *this)
        i.unbind();
}

void Item::reset_actor(const bool recursive) {
    set_actor_addr_direct(caf::actor_addr());