Experiment: Disabling per-section tidy

Introduce new variable, $wgMFTidyMobileViewSections, controlling per-section
tidy in action=mobileview. Default behavior remains the same, however we can
now experiment with it. Benefits include:
* Tidy sucks, make the world a better place without it
* It's slow - and since we can't afford caching every page, it affects
  performance profoundly
* Divs across sections will look reasonably

Change-Id: I8a95e7442100fc597ed2f7ded8b587709585f7d9
Merge "Experiment: Disabling per-section tidy"