Added missing options

Added option columns to IGridInstance

ui-grid/ui-grid.d.ts

@@ -483,6 +483,10 @@ declare module uiGrid {
          * use gridOptions.appScopeProvider to override the default assignment of $scope.$parent with any reference
          */
         appScope?: ng.IScope;
+        /**
+        * returns an array of columns in the grid
+        */
+        columns: Array<IGridColumn>;
         /**
          * returns the total column footer height
          */