Add Style and Theming!

[mckelveygreg]

We should make this look less generic? And correctly apply the MUI theme through out the site. I think the difficult part will be making the components in the exact same directory as they say in the docs so it will effectively overwrite it. I'm not very familiar with this process.
Link to docs: https://www.gatsbyjs.com/plugins/gatsby-theme-material-ui/#theming