Desktop ToC

[joepio]

In #100 @Wituareard created a Table of Contents component. This works for mobile devices, but not yet for desktop.

[joepio]

I'm also not entirely sure about the design as of now.

• The icon seems to suggest it opens top menu nagivation, but it's a ToC. Not sure how this should be improved.
• The spacing is a bit off I think
• The close button hides if user scrolls down, should be positioned at top right always

[Wituareard]

I changed the icon and made the head sticky so the heading and close button don't scroll.