add base16-default theme

I used the [base16 builder][1] inspired by monokai theme
to provide values from base16.

[1]: https://github.com/chriskempson/base16-builder

Demo below. I was unable to test this unfortunately, because I got some errors when changing themes in the standalone version and I didn't want my browser configs reset by using local .crx. Please notify me if something else is needed to make this work. Also, I was not sure if there are requirements or a convention for styles, so I just followed monokai theme to style keywords/types etc how I wanted.

I could also make more themes from the base16 project, but a brief look at some other schemes gave weird result. This is only the base16-default scheme, but I thought it looked cool.

![async-js-base16-zed](https://cloud.githubusercontent.com/assets/345808/3528080/93160ec0-078b-11e4-919c-d6bdc8247626.png)