DevTools: Split out the "workspace" and "bindings" modules from "sdk"

This allows for a better code structure and code reuse by alternative
devtools frontends.

R=pfeldman@chromium.org, pfeldman, vsevik

Review URL: https://codereview.chromium.org/471433004

git-svn-id: svn://svn.chromium.org/blink/trunk@180253 bbb929c8-8fbe-4397-9dbb-9b2b20218538