Add PageNavigationHelper

  * Highlights sidebar link if currently visited
  * Adds deprecated label in sidebar for pages having deprecated: true
  in their YAML front matter.
Use deprecated option in docs.yml to indicate deprecated docs

Deprecated docs will appear in the sidebar with a special label.
Port example code blocks to Bootstrap
Style tables
Fix path to favicon
Create /docs page
Style Back to Top button
Style headings
Style sidebar
Re-order API versions
Rename flavor_data to settings
Style index page
Remove deprecated source

Delete deprecated layouts

Delete deprecated stylesheets

Delete deprecated JavaScripts

Delete unused images
Reorganize assets
Add helpers for Page titles
Frontmatter based page titles
[wip] Breadcrumbs
Localize footer texts
Style lists
Format APIv3 content