Upgrade order item entity to support parent-child pattern

• Type: Sub-Task
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: None
• Fix Version/s: 2.1.1
• Component/s: Digital Store Management → Orders
• Labels: None
• Git Pull Request: https://github.com/marco-leo/liferay-portal-ee/pull/725

commerce order item should introduce parentOrderItemId field to make possible organizing records into parent-child hierarchy

IMPORTANT:
if parentOrderItemId == 0 there should not be ANY change related to business logic
if parentOrderItemId != 0 such entry represents CHILD ITEM which is applicable in product bundles where child item can refer to:

• option value that can be charged
• other non-product-bundle product SKU