function isCoveringExisting (newItem, existing) {
  return newItem.from <= existing.from && newItem.to >= existing.to
}
Examples:
existing: 10-20 | 10-20 | 10-20
new_item: 10-21 | 09-20 | 10-20
@param {MinimalSelectionItem} newItem
@param {MinimalSelectionItem} existing
@returns {boolean} returns true if the new item is covering the existing item