[not ready] Layer list up

![screen shot 2014-08-26 at 7 07 00 pm](https://cloud.githubusercontent.com/assets/108094/4053176/ba15a20a-2d75-11e4-99da-d49bd6a4aad3.png)

- User layer list from project.yml is properly displayed in layer list
- If there's a custom layer list, disable the change layer button.  

Todo:
- [ ] @samanpwbb layer list validation tests (in `test/style.test.js`)
- [x] @yhahn add client side tests

@yhahn I could use some pointers on how to approach testing for this.
Also add a testcase for your very first check -- where `layers` is not an array.