Scaffolds MJML and adds some initial templates and components.
Of interest are:
* src/Core/MailTemplates/Mjml/components/hero.js demonstrates how to create a custom MJML component. In our case it's a hero component with our logo, a title, a call to action button and an image.
* src/Core/MailTemplates/Mjml/components/head.mjml defines some common styling.
* src/Core/MailTemplates/Mjml/components/footer.mjml social links and footer.
