<td>Set both groups and items at once. Both properties are optional. This is a convenience method for individually calling both <code>setItems(items)</code> and <code>setGroups(groups)</code>.
Both <code>items</code> and <code>groups</code> can be an Array with Objects,
a DataSet, or a DataView. For each of the groups, the items of the
timeline are filtered on the property <code>group</code>, which