split up header & sharing image

* fixes #163

_src/_layouts/page.html

@@ -2,7 +2,7 @@
 layout: base
 ---
 
-<header role="banner" class="header" {% if page.image %}style="background-image:url('/assets/img/{{ page.image }}')"{% endif %}>
+<header role="banner" class="header" {% if page.header %}style="background-image:url('/assets/img/{{ page.header }}')"{% endif %}>
 
     {% include menu-main.html %}
 

_src/usecases.html

@@ -6,6 +6,7 @@ tagline: Where blockchains and databases meet
 description: For blockchain technology to go mainstream, it needs scale. At BigchainDB, we’ve taken care of that for you.
 
 image: photo4.jpg
+header: photo4.jpg
 ipdb: true
 
 intro:

_src/whitepaper/index.md

@@ -6,6 +6,7 @@ tagline: "BigchainDB: A Scalable Blockchain Database"
 description: 'This paper describes BigchainDB. BigchainDB fills a gap in the decentralization ecosystem: a decentralized database, at scale. It is capable of 1 million writes per second throughput, storing petabytes of data, and sub-second latency.'
 
 image: photo3.jpg
+header: photo3.jpg
 
 whitepaper:
     title: Whitepaper downloads