[#D3D-2581] Updates Shadowmap demo for atlas support
[#D3D-2581] Updates Shadowmap demo for atlas support

Use url option to test it:
?&atlas=1&lightNum=1
?&atlas=1&lightNum=2
?&atlas=1&lightNum=3
?&atlas=1&lightNum=4

cedricpinson/osgjs,cedricpinson/osgjs,jtorresfabra/osgjs,jtorresfabra/osgjs,cedricpinson/osgjs,jtorresfabra/osgjs