Sandbox alpha and beta skins from stable

* Add logic for beta and alpha skins into their own classes
* refactor MinervaTemplate to have two more
  overrideable methods - renderHistoryLink and renderMainMenu
* Add the logic for main menu headers into MobileTemplateBeta and
  reflect changes in MinervaTemplate

Change-Id: Ie848c604e25784b7c82175956e71a6f81edbbccb
Merge "Sandbox alpha and beta skins from stable"