If not empty, the class will be used to instantiate as a child control in the item cells of the column.
If the class implements {@link \Prado\IDataRenderer}, the Data property
will be set as the data associated with the datagrid cell during databinding.
The data can be either the whole data row or a field of the row if
{@link getDataField DataField} is not empty. If {@link getDataFormatString DataFormatString}
is not empty, the data will be formatted first before passing to the renderer.
