added the highlightLocation option identical to the LocateButton widget

I pretty much copy/pasted the naughty bits from [LocateButton](https://github.com/Esri/arcgis-dijit-locate-button-js/blob/master/js/LocateButton.js) and put them in the Geocoder widget. I suppose you could replace the `PictureMarkerSymbol` with a little house or something.

This is just to add some consistency between the widgets and save me/users from adding the location on our own if we're too lazy (I am really lazy).

I tested it locally and everything seems to work as expected.