If users are entering Lat/Lng values into the inputs it would be good if the marker was moved and the map redrawn to reflect those values.
In InputfieldMapMarker.js:
$lat.add($lng).change(function() {
var latlng = new google.maps.LatLng($lat.val(), $lng.val());
marker.setPosition(latlng);
map.setCenter(latlng);
});