Theme: editing support

[AustinWise]

The wiki should be writable from the website. Features include:

• Basic editing support, like a textarea and a submit button #16
• Edit screen should have a "Preview" button #51
• Some amount syntax highlighting?
• Maybe embed the VS Code editor into the page?
• Stretch goal that probably will never happen: a WYSIWYG editor

[rneswold]

A Preview button would be great!

I made several changes to fix some markup errors which resulted in several commits to the repo. I'd rather commit content that is proofread and correctly formatted.