fix datasource watch

this is addressing two issues:

1) fixed order of params when calling toDataSource in the $watch (see http://stackoverflow.com/questions/20982808/kendo-ui-chart-wont-update-using-angular); this would throw errors before

2) if there is a widget on the element which has a data source, update it with the
new data using a deep $watch; this addresses issues like https://github.com/kendo-labs/angular-kendo/issues/146 (for example, I believe there are others); using setDataSource since it seems to be relatively inexpensive and will refresh the widget (and the datasource was getting created anyway).


demo for chart + dropdown: http://jsbin.com/uqEgeCe/21/edit