Style site selector dropdown

Made dropdown receive chzn, and applied a dark style to the dropdown to
match the ui of the cms.

Before:
![1_05_13_12_13_pm](https://f.cloud.github.com/assets/984753/447860/11846ab0-b21d-11e2-8884-cae605ab4a6b.png)

After:
![1_05_13_5_05_pm](https://f.cloud.github.com/assets/984753/447861/13e6b77c-b21d-11e2-9bbe-b72d98278039.png)