Start using "wide mode" in the redesign branch

[mansona]

We recently added "full width" mode to the sidebar implementation on the ember-styleguide, we should bring this implementation to the website-redesign branch 👍

https://ember-styleguide.netlify.app/components/sidebar
ember-learn/ember-styleguide#478

[mansona]

@lukasnys is going to take a look at this one too 👍