Make product upload more flexible

[thomasjthomasj]

What does this do?

• Allows page types to be mapped to product types
• Allows users to set the selected shop page as the parent for product pages

  How should this be manually tested?

Upload some products on a site with the page type mapping, try to set the home page as a page

Related PRs / Issues / Resources?

Anything else to add? (Screenshots, background context, etc)