`Timeline` component

[fsbraun]

For the timeline component, I propose:

• Move heading, eyebrow and description outside the Timeline component, potentially into a full width section component (containing the <section> tag) and preparing for centered content (probably adding the .text-center class)
• Only allow Milestone components inside Timeline. The Milestone component replaces the current Card and CardInner.
• Timeline itself takes care of spacing.
• Milestones can be filled by any set of plugins. It's content defaults to left alignment.