Changed IGridOptions.data property to be any type

Curreng ng-grid documentation incorrectly lists out the possible data option values - it's actually either string or object reference. See https://github.com/angular-ui/ng-grid/issues/1033#issuecomment-37218058
Merge pull request #1866 from asaveliev/master

ng-grid: changed IGridOptions.data property to be any type