Add ability to delete a space that doesn't have a home page

Right now it's very hard to delete all pages in a space that doesn't have a home page (imagine 50 pages to remove), as you have to delete them one by one or script it. Alternatively you need to create the home page with artificial content to the be able to remove the children.

Goal:

• Add the delete menu entry even for page that don't exist. Ideally only show it if there are pages in that space. In order for the check to not be too costly we could run it only if the current page doesn't exist.
• On the delete template, modify a bit the text so that it matches the use case. For example "Are you sure you wish to move this page to the recycle bin?".
• Modify the "delete" action to support this use case. Right now we get a 404 when going to https://domain/xwiki/bin/delete/SpaceThatDoesNotExist/WebHome, we should check if children exist before sending back an error