Include a more engaging dataset in chapter 1

[joelostblom]

We used cars for now to get the material out, but let's see if we can find a data set that more closely relates to the narrative and the students. This will also help solve several related issues. A clearer more motivating question can be introduced so that they students work with this in their mind as they are learning to create a viz. That can also help clarify the need to build up the charts one step at a time (but also consider showing the entire chart first).