@craigspaeth Fix safari flickering when modifying the hero element while it is covered

Repro: In safari, scroll to the bottom of the page. When the 'bottom-mode' class is added or removed from the hero unit, the hero will be z-indexed to the top for a split second causing an odd black flash.

To fix this, we hide the dom node and then in a setTimeout (a _.defer), we add the 'bottom-mode' class. This fixes the flickering. WTF SAFARI.

Apparently, if you modify a dom element in Safari temporarily gets z-indexed to the top (?)