[blog] New post folder does not move collateral inside

[preaction]

If we create a new post, that post gets created in a folder like /YYYY/MM/DD/default-title. As we develop that post, we may add collateral images and documents to the folder. If we change the title of our post, which we probably will, the new folder created will not contain our collateral, and then the clean up of the old folder will delete that collateral entirely, potentially losing work.

We should either rename the folder, or otherwise ensure that the collateral is moved with the post.