Alpha: Move dynamic section loading from beta to alpha

Whilst this is not a priority this risks breaking and also
adds an element of inconsistency between alpha and beta
Already there are various bugs (e.g. bug 44562)
* only define mf-search.js once - in stable module
* don't define mf-toggle.css twice - it's in mobile.styles
* define dynamicPageLoadsEnabled in history module
* Remove repeated code in mf-history-jquery.js
* Now jQuery is ubiquitous add to closure in mf-history.js
* Remove traces of lead section toggling code from toggle.js
Change-Id: If29a84ea8417cf8883c351ab342414cbab1cbaca