Scrollbar Issue in Responsive Layouts

This is a fix to the issue described in title.
In source/common/javascript/generated/common.js, I added a JS function calculating browser's scrollbar width.
In source/common/javascript/generated/view-responsive-layouts.js, I modified WebDeveloper.Generated.initialize function to add scrollbar's width to iframe's width & height and to add attribute scrolling="yes" to each iframe.
In source/common/style-sheets/generated/view-responsive-layouts.css, I added overflow:scroll in iframe's style.