tile traces should have reasonable default behavior when given cf or Zelig objects

[chrisadolph]

When a tile trace is passed a cf or Zelig object without much in the way of user inputs, it should have a reasonable default behavior.

Tile traces have no facility for this now, as you need to manually extract stuff from your simulator and plug in to the correct inputs. In other words, if you pass a cf object to ropeladder() as the x input, it should assume you want to plot the pe's and ci's with the names given to each scenario in the cf object. Would require implementation of Issue 15 above.

[aserlich]

I started thinking about how to implement default behavior for ropeladder when it encounters a counterfactual object. The general way this is done is with methods. So there would be two methods for ropeladder 1) ropeladder.default and 2) ropeladder.counterfactual. The unusual issue with this is that ropeladder by default has no user specified inputs. The other way to do this would be to have if statement checks within ropeladder. That is less elegant, however. What do you think?