Redesign index and archive lists of posts

* No longer include an excerpt of a post
* Make a bigger feature out of the post images, use bigger images and
place text over the top
* Use a dark grey background instead of sky blue to give content more
prominence.
Use a large blurred background

* Give each post and page a feeling inspired by the content by using a
specified background image
* Blurring large images on the fly will cause CPU spikes, instead
create low quality blurred images
Fix text underline on masthead links
Don't include post pages in next/prev navigation