Can I extend the PointCloud class to add more properties

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

I wanted to add more properties to the PointCloud class and still make sure all point cloud related functions can work properly, such as **o3d.io.read_point_cloud** and **o3d.io.write_point_cloud**.

```python
class SegmentedPointCloud(o3d.cpu.pybind.geometry.PointCloud):
def __init__(self, points, normals, colors, MORE_PROPERTIES):
super(SegmentedPointCloud, self).__init__()
self.points = points
self.normals = normals
self.colors = colors
self.MORE_PROPERTIES = MORE_PROPERTIES
```