allows syncing two copies of data (all or just a part of it) from one DataCollection to another
| source | object | the object that the method is assigned to | 
| filter | function | the filtering function | 
| silent | boolean | if you set the parameter to `true`, the object won't be repainted after synchronization | 
// full copy
$$("list").data.sync(data);
 
// partial copy
$$("dview").data.sync(data, function(){
    this.filter(function(data) {
        return data.year > 1994;
    });
});