DAR-264: As Wikia we want to define a new minimum article body area and right rail

NEEDS THUMBS UP FROM CONTRIBUTION TEAM MEMBERS BEFORE MERGE

https://wikia-inc.atlassian.net/browse/DAR-264

Creates a flag for responsive layout style and injects a new responsive.scss file into head if the responsive layout is enabled. For now, only content pages that aren't main pages and hub pages will get these new styles.

Changed the width of the right rail from 320px to 300px and re-styled the main content area so that the article content can be fluid width.

See also: https://github.com/Wikia/config/pull/130