Making WinJS global optional and adding 'onefile' grunt task

Added onefile grunt task which allows you to build a single-file build of WinJS from any leaf node, for example:

  > grunt onefile:WinJS/Controls/AppBar

Also made publishing of WinJS global optional (base / ui / WinJS / <files generated by onefile task> all still publish it as the last step while loading). This opens us up to building WinJS in a manner where it could be deployed SxS.