feat: 'addon' property support

feat: 'addon' property support

..to be able to render something like OK button to timepicker:
```
            <TimePicker
              allowEmpty={false}
              addon={panel => {
                return (
                  <div className="row">
                    <a role="button" className="btn btn-sm btn-default" onClick={() => panel.close()}>
                      {__('OK')}
                    </a>
                  </div>
                )
              }}
            />

```