Alternative toolbar flicker solution

Alternative solution to toolbar flicker.

#2542050: Toolbar implementation creates super annoying re-rendering. is much better (no flicker at all) since it's pretty invasive I thought this had better chances to make it earlier in the meantime.

There are various improvements over core solution, mainly there is only one reflow insead of the current 3 (coming from: toolbar, menu tray, and escapeAdmin). It does kinda spoil the experience on Firefox since there is currently no flicker there, with this patch it's at the same level as chrome. 1 reflow.

• Hide the toolbar by default so computation is done before the toolbar is rendered, hence only one reflow
• Assume browser has JS enabled (same strategy as the has_js cookie killer patch #229825: backport "$_COOKIE['has_js'] must die" patch to 7.x) (the js class is added too late for .js-hide to be useful)
• Use requestAnimationFrame() to batch style changes. Init behavior goes from 60ms to under 20ms on desktop. IE10+ only though.
• Mess with weights of the toolbar scripts to make sure it's always rendered early, prevent toolbar render delay when there is a ckeditor on the page for exemple. Won't need this when #2367655: Control the list of behaviors run by Drupal.attachBehaviors goes somewhere.