[Child pages] Allow sorting of child pages

🚧 The issue is still a work in progress.

**Is your feature request related to a problem? Please describe.**
When adding new pages as children to a page, the order can't be set, and there isn't a consistent way in which the order changes.

**Describe the solution you'd like**
When a page has child pages (a page has set it as a parent page), sorting the child pages in the admin interface should be possible.

**Describe alternatives you've considered**
In other places, items are ordered based on the last edited date.
At least this way of ordering items could be implemented so a framework for ordering exists and a way for users to edit items.

**Additional context**
We would need a design and/or workflow for this to know how these changes should look like.