Styles admin nav toggle as a link

 modified:   app/assets/stylesheets/base.css.scss
Helper to format a published article's date

 new file:   app/helpers/article_helper.rb
 new file:   spec/helpers/article_helper_spec.rb
Simplifies the admin articles index

 modified:   app/views/admin/articles/index.html.erb
Admin articles index links to article on public route

 modified:   app/views/admin/articles/index.html.erb
Changes password field in login template

 modified:   app/views/admin/sessions/new.html.erb
Forgot to whitelist article form parameters

 modified:   app/controllers/admin/articles_controller.rb - Capybara specs would have helped perhaps
Strong params for an Article, categories should be specified as an array

 modified:   app/controllers/admin/articles_controller.rb
Adds a field to the Article form for adding Categories

 modified:   app/views/admin/articles/_form.html.erb - uses collection_check_boxes helper
Adds tag_ids to whitelisted params in Admin::ArticlesController

 modified:   app/controllers/admin/articles_controller.rb
Adds a field to the Article form for adding Tags

 modified:   app/views/admin/articles/_form.html.erb - uses collection_check_boxes helper
Specifies extra links to appear in admin dashboard

 modified:   app/views/admin/dashboard/index.html.erb
 modified:   spec/requests/admin/admin_pages_spec.rb
Admin::CategoriesController and TagsController must extend the Admin::BaseController

 modified:   app/controllers/admin/categories_controller.rb - otherwise the actions
              of these controllers were not protected by the :authorize method
 modified:   app/controllers/admin/tags_controller.rb
Category and Tag page specs need to sign in a test user before running specs

 modified:   spec/requests/admin/category_pages_spec.rb
 modified:   spec/requests/admin/tag_pages_spec.rb
Adds some styling divs to admin dashboard

 modified:   app/views/admin/dashboard/index.html.erb
Adds a containing div to admin dashboard links

 modified:   app/views/admin/dashboard/index.html.erb
Application layout loads a separate stylesheet if in the admin namespace

 new file:   app/assets/stylesheets/admin.scss - styles specific to admin site
 modified:   app/views/layouts/application.html.erb
Wraps the admin dashboard div elements in link_to blocks to create clickable 'boxes'

 modified:   app/views/admin/dashboard/index.html.erb
Always shows the Categories heading in sidebar

 modified:   app/views/layouts/_sidebar.html.erb
Adds specs for Article-Category association

 modified:   spec/models/article_spec.rb
Adds before_save method to Article model, to assign a default Category

 modified:   app/models/article.rb - if no categories are assigned the default
              Category 'Uncategorised' is assigned (and created if required)

Specs would be nice, but Article specs that test the default category will
clash with category specs and it's `.with_articles` method - they are too
tightly coupled at the moment