Geometrical segmentation (vertical & horizontal ) on point clouds

### 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

@adamlofts @equant @benjaminum @FreakTheMighty @gsakkis

Hello. I saw in one of your notebooks the plane segmentation on point clouds which is really great.
https://github.com/isl-org/Open3D/blob/master/docs/jupyter/geometry/pointcloud.ipynb

I would appreciate if you inform me if there is a way with Open3D to do segmentation of horizontal and vertical point clouds. To get horizontal point clouds one color and other color for vertical point clouds.

I look forward to hearing from you and thanks in advance!!!