Use Warden to authenticate people.

I couldn't get my head wrapped around OAuth without some sort of authentication mechanism so I did this first.

I was shooting for the smallest, semi-functional, merge-able chunk out of what we discussed and I'm submitting this now to see how it fits.

I had to remove the turbolinks tags because turbolinks wasn't in the Gemfile. I wish I had those changes in a separate commit but that didn't happen. :grin: