Fixed duplicate site title call

I suck at giving decent requests: 

Originally in source/_includes/header.html, the following was being called:
<h1><a href="{{ root_url }}/">{{ site.title }}</a></h1>
...code...
{% include custom/header.html %}

I propose that it is moved to just the header.html to, avoid confusion and duplication of site title. 
{% include custom/header.html %}