Port theme to Drupal 8

Now that we have a stable beta release, it's time to start porting the theme to Drupal 8. This may take some time due to the changes in themeing Drupal 7 and 8.

Development path

This issue will stay open until a stable release is available so others can follow the development path. 8.x-2.x-dev is the initial development release to get things started.

Things to consider while porting to Drupal 8

1. Drupal 8 outputs semantic HTML5 markup by default, whereas Drupal 7 used XHTML
2. Drupal 8 uses jQuery 2.x, so no need for the theme to retrieve the jQuery 2.x library from cdnjs.cloudflare.com
3. Drupal 8 introduces Twig in place of PHPTemplate
4. In Drupal 7 if you wanted to add CSS or JS to a particular page, you'd use the drupal_add_css() and drupal_add_js() functions, respectively. This is now replaced by attaching JS/CSS assets in the #attached property of a render array using libraries. This will change how additional UIkit components are added to pages.
5. Drupal 8's CSS (file) structure is based on SMACSS & BEM.
6. Drupal 8 ships with Classy, a core base theme that injects classes into markup, and includes corresponding CSS. In progress: This will replace many preprocess functions and CSS files which were previously included in core modules.
7. Drupal 8 moves CSS classes from preprocess functions to Twig templates.
8. Drupal 8 uses breakpoint media queries to control how the site looks on different devices.

This list was taken from Theming differences between Drupal 6, 7 & 8, which includes additional things to consider. The above list is the main things we need to look at when porting to Drupal 8.

There is also an article over at Lullabot.com by Marc Drummond that provides excellent insight into the new base themes introduced in Drupal 8: A Tale of Two Base Themes in Drupal 8 core. I'll also refer to this when porting to Drupal 8.