Enable Site Builder to use/copy the main website header

Right now, the site builder can create custom headers. However, you're unable to create a variation of the main website header. There are two problems in the way: 1. You need to manually recreate the main header 2. You can't use all of the main header's features (e.g., the main header's account widget is unavailable, along with everything else that's in the main header editor) I suggest adding the ability to create a copy of the main header in the site builder. Ideally, all of the features of the main header customizer would be available in site builder too.