When clicking on the Add page button, remember the current page

[talyguryn]

It is necessary to set the current page as a parent in the parent page selection field

Steps to reproduce: - run docs instance - auth via /auth - go to some existing page - click "Add new page" - You will see that new page will be created in the "Root", but it would be much more convenient if there was a page that the user was on before

[neSpecc]

I'm not sure, that it is the best solution.

The Add page button displayed at the Site Header, so it is not related to the current page. And it could be confusing for user why the new page is creating not at the root.

As a workaround I'd suggest to add another Add page button somewhere at the Article block