Store story data as markdown.

* Converts HTML to markdown on save.
* Converts markdown to HTML on render.
Fix blockquotes not centering.
Flesh out editor button styles.
Setup editor options.
Reset possible markdown outputs.
Tweak story body formatting.

* Add styles for headers.
* Adjust margins.
Add margin near end of story editor.
Remove fullscreen component from editor.

* Fullscreen disables keyboard input.
Refactor estimate reading time to not require html2text.