Tools improvement

Adding a WinJS application to quickly test a babylon scene on tablets.
Improving OurBabylonJSServer demo file dectection, it is now listing all folders containing .babylon files.
Adding a babylon sandbox on the server and inside WinJS App.
Adding a loading message on server and WinJS App.
Adding a folder to automatically add content to WinJS App ( @gwenael-hagenmuller )
Automatically build ourownbabylon.js when build WinJS App ( @gwenael-hagenmuller  )