Restore persistent ID

[malberts]

AC:

• trigger on page restoration hook
• save the old page's persistent ID on the (new) restored page

[malberts]

Marked as blocked, because I have not been able to reproduce a scenario where an undeleted page gets a new page ID (as per #32 (comment)). However, according to the docs and the hook it is possible, but until I know how to do that, I don't want to code blindly and just mock test data to be in this state.