naive collection cascade destroy

bookshelf.collection.cascade.destroy.js

async destroy (options = {}) {
  const destroyed = this.clone().reset()
  destroyed._events = this._events // Copy referens to events
  if (!this.length) return destroyed

  await destroyed.triggerThen('destroying', this, options)
  
  for (const model of this) {
    await model.destroy(options)
    destroyed.add(model)
  }
  
  await destroyed.triggerThen('destroyed', destroyed, options)
  
  return destroyed
}