Added the MinimalMainPage extension which removes a large portion of the...

... main page chrome in order to allow more space on promotional wikis. This is designed for use mainly by wikis that Wikia creates to promote Wikia functionality. It will soon be toggleable by the wgEnableMinimalMainExt Wikifactory variable. Ads can be suppressed on the MinimalMainPage by setting wgMinimalMain_hideAds to true in Wikifactory.
Can we name this `wgMinimalMainPageHideAds`?