Corrected error:

When calling:
```bash
rosrun object_recognition_core detection -c `rospack find object_recognition_tod`/conf/detection.ros.ork --visualize
```

got this error:

```
Traceback (most recent call last):
  File "/home/destogl/Workspace/ros/catkin_ws/src/object_recognition_core/apps/detection", line 21, in <module>
    plasm = create_plasm(ork_params)
  File "/home/destogl/Workspace/ros/catkin_ws/src/object_recognition_core/python/object_recognition_core/pipelines/plasm.py", line 66, in create_plasm
    cells[cell_name] = cells[cell_name](cell_name=cell_name, n_inputs=n_inputs, **ork_params[cell_name])
  File "/home/destogl/Workspace/ros/catkin_ws/src/object_recognition_core/python/object_recognition_core/io/voter.py", line 37, in __init__
    ecto.BlackBox.__init__(self, *args, **kwargs)
  File "/opt/ros/groovy/lib/python2.7/dist-packages/ecto/blackbox.py", line 248, in __init__
    self.__class__.__name__) + 'needs to be decorated with @classmethod or @staticmethod.')
ecto.blackbox.BlackBoxError: The "declare_cells" function of the BlackBox Aggregator needs to be decorated with @classmethod or @staticmethod.
```

This happens because inherited methods have attribute @classmethod .