Get delete abilities working, add created_at date next to username on index

@travisvalentine There are still tiny bugs around allowing users to do certain things. For example, a currently logged in user could create a new user while logged in so I patched that up. I think any user could delete another currently with some curl action, though I'm not positive. We should just comb through and find all of these gotchas before allowing any real users to sign up. 
Would we wanna be able to delete others in the UI? If so, then maybe:

```
@user = if current_user.admin?
  User.where(username: params[:id]).first
else
  current_user
end
```