Issue 855989

* optimize css in build process with modified clean-css https://github.com/GoalSmashers/clean-css

* aggregate css in /style folder to keep relative resources path

* not aggregate share styles since its packaged in webapp-zip and each share style is located in its subfolder, its not trivial to reference every resources without changing the css definition.

* separate CSS optimize from JS for performance evaluation

* keep linebreak for debug