Images added with drag and drop to XhtmlString properties added to start page's content folder

Description

Steps to reproduce:

1. Open any page with the Content Area property.
2. Create a new `Editorial Content` block.
3. Click `Quick edit` on the newly created block.
4. Drag and drop an image from your local disk to the XHTML property.
5. Navigate to the block and check it's in the `For This Block` folder.

Expected result:

Images are created in the `For This Block` folder.

Actual result:

Images are created in the `For this page` folder.