Enhanced RC: Optimization of the initial collapsing

Enhanced RC: Optimization of the initial collapsing

* mediawiki.special.changeslist.enhanced: Hide the rows that would be
  hidden by jquery.makeCollapsible with CSS to save us some reflows
  and repaints. This doesn't work on browsers that don't fully support
  CSS2 (IE6), but it's okay, this will be done in JavaScript with old
  degraded performance instead.
* jquery.makeCollapsible: Allow the element to be hidden on initial
  toggle without removing and adding back the 'mw-collapsed' class.
  This wasn't a performance issue in the past, but now it would
  cause the newly added CSS rules to have to be recalculated (although
  browsers seem to optimize it and avoid repaints at least).

Bug: 51749
Change-Id: I3823c2a67d524e6598e2437e1dd065659d1c7e41