Fix Object 7 has no method 'setAttribute' error

Fixes an error where `angular.forEach` iterated over the `length` attribute on the jQuery object returned as the `columns` array in `self.setDraggables`, throwing an error looking like (for example) `TypeError: Object 7 has no method 'setAttribute'`. Simply adds a `jQuery.makeArray` wrapper, so the `columns` array is a plain JS array, not a jQuery object, fixing the problem.