This makes the editor experience much better (by subjective measures). Now instead of a WYSIWYG editor, we have a markdown code editor, and we also have the ability to view documents without editing them.
While I was at it, I fixed a bug where if you didn't edit a document at all, it would save blank. This was fixed as a happenstance from the switch.
Also included here is making the UI work with Javascript disabled. If you don't have JS, you will get a textarea which allows editing the markdown directly. If you do have JS enabled, you'll get a smarter editor.
Reviewed-on: #3
