Add basic Benefits component

[jxnblk]

• Adds Benefit component where content is shown in a single row as "cards"
• Adds Link component – using this instead of Button for the links in content
• Checks for absolute URLs in Link and Button to avoid warnings from GatsbyLink
• Adds inline and as props to MarkdownText to allow the content to be rendered as a heading; definitely would like to know what you think about this approach
• Passes className to MarkdownText; I'll merge your changes before this one and address any potential conflicts

[gatsby-cloud[bot]]

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gatsby-starter-landing-page

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