Add shadow to tabbar & navigation toolbar similar to shadow file tree view has

TBR @cleercode

Especially noticeable with light editor themes

![screen shot 2014-06-17 at 1 17 35 pm](https://cloud.githubusercontent.com/assets/5606182/3306006/bfb559e4-f65c-11e3-9ffa-000d1d0b6c81.png)

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![screen shot 2014-06-17 at 1 19 38 pm](https://cloud.githubusercontent.com/assets/5606182/3306010/c70cb570-f65c-11e3-922c-9e5024c543c2.png)