MSI integration write

[vadimjustus]

Description

Writing stock information to default stock by data which provide by the origin catalog inventory module.

Manual testing scenarios

1. Edit quantity of stock for a product in Magento backend
2. Information should be persisted also in the MSI default stock

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[naydav]

Will be finished in
#198