add support for unpublished drafts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not working on right now as unpublished so they don't clutter the site while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.
Merge pull request #2164 from mrtazz/draft-unpublished
Update history to reflect merge of #2164 [ci skip]