Markdown preview

[eevee]

trafficstars

Only place markdown is actually used atm is when submitting a comic page, so, do it there.

For the fancy-pants version, do I ajax this or find a js renderer that's hopefully close enough to the python one? :/

Also, minor problem: how do you preview when the form includes a file upload? Just say no-js can suck it? Ugh.

Maybe just adding edit support would make this easier. Can always add the audit trail later.