Rebase on top of D504.

Added missing license.

Minor SQL formatting changes.

Done all requested minor fixes

The test passed. However, please make these minor adjustments.

Done all requested improvements

I haven't executed the test plan yet. Please make the proposed corrections/answer questions.

In D497#10224, @alex wrote:

In D497#10220, @erik wrote:

maybe, test plan should include requirement to have checked "Use Cron to run Scheduled Tasks" - otherwise visible email queue is usually empty.

Done.

detected error, not related to current task when creating product
Product was created by default in home category, so not shown on front-end. So, manipulating with product categories on product edit sections tab,
i got SQL error when trying delete product section.

RuntimeException: Column 'CategoryId' in where clause is ambiguous

I'll create a separate issue about an SQL error during removing a category association from the category item (e.g. product).