Adds styling for the Tag/Category index views

 modified:   app/assets/stylesheets/base.css.scss
 modified:   app/views/categories/index.html.erb
 modified:   app/views/tags/index.html.erb
Promotes the list styles in sidebar element to site-wide

 modified:   app/assets/stylesheets/base.css.scss
Makes the site footer "sticky" for when content is short

 modified:   app/views/layouts/application.html.erb - puts page content, except
              footer in a page-wrap div

 modified:   app/assets/stylesheets/_variables.css.scss - defines the footer height
 modified:   app/assets/stylesheets/base.css.scss - page-wrap has a negative bottom
              margin equal to the footer height. page-wrap also includes clearfix so
              that content does not run into footer.
Adds Google Analytics to application layout

 new file:   app/views/layouts/_google_analytics.html.erb
 modified:   app/views/layouts/application.html.erb
Creates route for Article feed

 modified:   config/routes.rb - has it's own path "/feed" as using the root path
              would look strange, ie "/feed.atom" looks nicer than "/.atom"
Creates controller action for feed and Atom builder

 modified:   app/controllers/articles_controller.rb
 new file:   app/views/articles/index.atom.builder
Fixes issue that was halting spork from starting

 modified:   spec/support/have_title_and_content.rb - unnecessary require (and
              incorrect due to folder structure)
 modified:   spec/support/shared_examples_grouping.rb
Fixes Article model spec for when 'Uncategorised' Category exists

 modified:   spec/models/article_spec.rb - other specs may have created this
              when an Article is saved, so check the test DB if it exists first
Fixes Article page specs, since they were changed

 modified:   spec/requests/article_pages_spec.rb - Comment form is now in a
              section element (this spec overlooked when spork issues arose)
Renames shared examples for static pages (no longer used, but just in case)

 renamed:    spec/support/pages_shared.rb -> spec/support/shared_examples_static_pages.rb
Requests were not making it to root as the articles route caught them, but...

 modified:   config/routes.rb - better to be correct
Handles feeds in the Category and Tag controllers

 modified:   app/controllers/categories_controller.rb
 modified:   app/controllers/tags_controller.rb

Refactor plzkthx
Merge branch 'article-feed' into develop-blog

 Creates a feed for the most recent published Posts
 Feeds for Category and Tag Posts (they are not linked on any view yet)
Modifies specs for a grouping model and related Articles

 modified:   spec/support/shared_examples_grouping.rb - creates Pages and Posts
              to check scope `.with_articles` gets them all, and (future) scope
              `.with_posts` only gets Posts
Specifies table names in Grouping Concern joins and scopes

 modified:   app/models/concerns/grouping.rb - `created_at` is ambiguous, and
              other table names specified for consistency
Specs a new scope in the Grouping Concern that returns unique groupings with published Posts

 modified:   app/models/concerns/grouping.rb
 modified:   spec/support/shared_examples_grouping.rb