content: Add lazy UI loading page

Port it from the page on blogo. Needs a link somewhere.
content: Add a 'documentation' page
content: Link the comment policy from the about page
theme/template: Optionally show the abstract of pages
content: Add an abstract to the lazy loading page
theme/css: Fix the selector for article-abstract

We are using an id, so we don't need path specificity.
theme/templates: Add proper titles to all pages
content: Add draft of the GDK/GL article
content: Add GDK threading article