Create and migrate to custom `<Icon>` component in Markdown

[parlough]

Create a new <Icon> component that can be used from Markdown content loaded with Jaspr Content. Then migrate content across the site that uses icons with manual HTML to the new component.

It should:

• Use the existing MaterialIcon Jaspr Component if possible.
• Require an icon id.
• Require a label for accessibility.
• Accept an optional size parameter.
• Accept an optional filled parameter (defaults to false).
• Accept an optional class parameter for additional customizability.