function isColumnVisible(colDef) {
        return colDef.visible === true || colDef.visible === undefined;
      }
@ngdoc method
@methodOf ui.grid.uiGridGridMenuService
@name showHideColumns
@description Adds two menu items for each of the columns in columnDefs.  One
menu item for hide, one menu item for show.  Each is visible when appropriate
(show when column is not visible, hide when column is visible).  Each toggles
the visible property on the columnDef using toggleColumnVisibility
@param {$scope} $scope of a gridMenu, which contains a reference to the grid