Ordinal scale reverse

Ordinal Y-scales on XY Plots will have their range reversed from other scale types so that the domain is read top-down rather than bottom-up

![screen shot 2014-11-06 at 3 17 42 pm](https://cloud.githubusercontent.com/assets/1448299/4945769/298d61d6-660b-11e4-8b18-3b7b17903e5a.png)

Closes #1189