Add sandbox ID to the Make theme header

[iandunn]

The make.wordpress.org sites aren't showing the sandbox IDs in the <title> right now, so there isn't a quick/easy/reliable way to tell if you're hitting your sandbox or not. It should show the ID, just like the areas that use the global header do.

[iandunn]

Attached patch. Instead of just duplicating the global header logic in the Make child theme, I centralized it and then set both instances to call the central function.

[nacin]

All sites use the global header.php for their header. The only exception is the placeholder Twenty Eleven child theme currently powering make.wordpress.org. That child theme should be updated to use header.php and set $pagetitle. That said, there aren't actually any other current plans to use Twenty Eleven on wordpress.org, so this can just be ignored until make.wordpress.org gets redone to use the global header.