Move sky-box,-button,-checkbox,-radio out of their directories
Move sky-box,-button,-checkbox,-radio out of their directories

Instead of having a separate directory for every Sky element, we should just
put them in the general framework directory. Once the framework is more
complicated, we'll probably want to organize it a bit better, but for now there
aren't enough files to justify having so many directories.

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/874303003

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