WIXFEAT:4505 - WixHttpExtension for URL reservations

I tried to find all the places to add the new extension and implement everything, but I might have missed something.

I would like to port this back to v3.x.
Would be good to have a comment explaining what the `*` is here. I was really confused until I got around to reading the .xsd comments. A couple lines of text here would go a **long** way. :smile: