add support for unpublished drafts

I keep all my ideas for blog posts as drafts in my draft folder. However I'm
only really working on a couple at once. This let's me mark drafts that I'm
not working on right now as unpublished so they don't clutter the site while
I'm checking on the other drafts.

I only added feature tests since I didn't quite grok if there was something
to add to the unit tests. Please let me know if I should add tests in there
as well.