Added adapter factory for customize the list view elements in the dialog

[giacomomagini]

When you declare and configure the searchable spinner, can specify how instantiate the adpter for list view in the dialog. Below an example:

mSpinner.setDialogAdapterFactory(new SearchableListDialog.AdapterFactory() {
@OverRide
public ArrayAdapter newInstance(List list) {
return new MyCustomArrayAdapter(getContext(),list);
}
});

[velval]

This should be merged to allow custom adapters on the ListView