Adjusting the hierarchy and names of generated PMPro pages

[kimcoleman]

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Changes proposed in this Pull Request:

Now generating pages as follows:

Membership Account page is parent of the: Billing, Cancel, Orders, and Profile Edit page.
Membership Checkout page is parent of the Confirmation page.
Membership Levels and Log In are top level pages.

Other information:

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• Have you successfully run tests with your changes locally?

Changelog entry

• ENHANCEMENT: Updated the hierarchy and names for generated PMPro pages as part of optional initial setup steps.

Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.