Move page #post helper to encapsulate image references

Ref #143
- Fixes header images for static pages

page.hbs

@@ -3,6 +3,9 @@
 {{! This is a page template. A page outputs content just like any other post, and has all the same
     attributes by default, but you can also customise it to behave differently if you prefer. }}
 
+{{! Everything inside the #post tags pulls data from the page }}
+{{#post}}
+
 <header class="main-header post-head {{#if image}}" style="background-image: url({{image}}){{else}}no-cover{{/if}}">
     <nav class="main-nav {{#if image}}overlay{{/if}} clearfix">
         <a class="back-button icon-arrow-left" href="{{@blog.url}}">Home</a>
@@ -14,7 +17,6 @@
 
     <article class="{{post_class}}">
     {{! Everything inside the #post tags pulls data from the post }}
-    {{#post}}
 
         <header class="post-header">
             <h1 class="post-title">{{title}}</h1>
@@ -24,7 +26,7 @@
             {{content}}
         </section>
 
-    {{/post}}
     </article>
 
 </main>
+{{/post}}