Ensure new identical field order in both unit config and database table.

1. extract "\ChangeLogHelper::getUserFields" from the "\ChangeLogHelper::getAddFields" for easier customization
2. change cache key of the \ChangeLogHelper::getAddFields method to include also session_id

Rebase on top of D504.

Added missing license.

Minor SQL formatting changes.

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

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).