Remove apostrophes from comments.

The Emacs SCSS mode flips out when there are apostrophes in
comments for some reason.
Style topbar.
Add sample screencasts.
Add topics to group challenges.
Replace home page.
Widen page.
Fix topbar.
Reorganize home page.
Clean up pages.
Fix button styling.
Add topics to articles.
Create importer to load curriculum.
Add list of topics.