Merge change 2146 into donut

* changes:
  Implements the basic structure for providing localized documentation; the site tabs are now in a separate file to ease the translation process, the language selection menu has been added to the header, scripts have been added to dynamically switch the language of the site tabs and dev guide side navigation and save the language preference in a browser cookie, and some of the functions in macro.cs have moved into customization.cs.