Adding support for disqus / google plus for comment system

 - create new form partials for disqus & google plus
 - allow comment/uncomment of desired commenting system
Give option to use an image both as a cover-image and as a post image

 - an alt of 'cover-image' combined with another text will use the said image as cover and will also be embedded in the post body
 - use of 'cover-image' alone as alt will just use this as cover image of your post
CSS to center the Page number using default pagination helper
Added package.json to please latest Ghost release