correct for value for defualt tax of a zone to match input id

Before:

![screen shot 2014-09-27 at 6 04 40 pm](https://cloud.githubusercontent.com/assets/3117356/4432764/7ed975a0-46ab-11e4-9d48-71738a156b8f.png)

After:

![screen shot 2014-09-27 at 6 05 41 pm](https://cloud.githubusercontent.com/assets/3117356/4432767/a113c1ca-46ab-11e4-8d94-2085ed7c8147.png)


The `for` attribute of the default zone tax label now matches the `id` attribute of the input checkbox for the default tax zone.