Bug 1100643: Integrate customCSS

Removed several unused classes: .quicknav, endImageWrapping, sidebar-box, tab-content-box, action-driven.

Reduced specificity of classes reliant on .redesign class: .spec-* and .htab.

Updated styles: fancyTOC, smallTextMultiColumnBox, standardSidebar.
Ooooohhh, flexbox. Nice!