[wix-devs] Redesign RemotePayload

[Sean Hall]

I created a WIP to redesign RemotePayload at
https://wixtoolset.org/development/wips/4183-redesign-remote-payload. It
also gets rid of the magic behavior of using the first payload for the
package payload if neither SourceFile nor RemotePayload is specified. I
associated it with 4183 (Allow separation of package and payload in chain)
since that's how I'm proposing to change it, but that's not really what I'm
interested in if we want to do this differently. Any feedback?