Band aid header

[dipree]

Making sure every page uses a layout with the much needed header instead of using anything from the template.

Re-did:

• layout with toc but not a component
• simple layout w/o toc (special treatment for source)
• hero layout

[joshblack]

Just one question on the layouts, is it possible for us to use a default layout for these so we don't have to wrap each page? e.g. https://www.npmjs.com/package/gatsby-plugin-mdx/v/1.0.13#default-layouts or do we need to add explicit layouts for each page?

cc @camertron curious what you'd recommend 👀

[dipree]

@joshblack I tried that first but it's resulting in a number of errors when not making any other changes. It's also worth noting that all the component pages already use a layout, but not the "default" pages and some index pages had the index layout, some had not. But agreeing with you that it would be the better approach.