Add a private global variable to track version
Add a private global variable to track version

This variable is useful for sites which measure usage of various JS
libraries. WinJS did not have a globally exposed variable, so sites could
not reliably track different versions of WinJS. This change
leverages the existing string replace grunt task and exposes
WinJS.Utilities._version.

Guadzilah/winjs,KevinTCoughlin/winjs,nobuoka/winjs,jmptrader/winjs,PaulWells/winjs,kevinwsbr/winjs,IveWong/winjs,GREYFOXRGR/winjs,kevinwsbr/winjs,nobuoka/winjs,KevinTCoughlin/winjs,nobuoka/winjs,edrohler/winjs,edrohler/winjs,jmptrader/winjs,KevinTCoughlin/winjs,gautamsi/winjs,PaulWells/winjs,gautamsi/winjs,GREYFOXRGR/winjs,kevinwsbr/winjs,Guadzilah/winjs,gautamsi/winjs,grork/winjs,rigdern/winjs,IveWong/winjs,ladyinblack/winjs,CensoredUser/winjs,grork/winjs,rigdern/winjs,CensoredUser/winjs,PaulWells/winjs,ladyinblack/winjs,GREYFOXRGR/winjs,edrohler/winjs,CensoredUser/winjs,grork/winjs,rigdern/winjs,jmptrader/winjs,ladyinblack/winjs,Guadzilah/winjs,IveWong/winjs