Replace open3d with pyvista

[isaaccorley]

Refactors point cloud plotting in the torchgeo.datasets.IDTReeS dataset to use pyvista instead of open3d

Note: Currently figuring out the min version which passes tests.

See #662

Example:

https://user-images.githubusercontent.com/22203655/178155777-dac2e462-d978-4005-9412-3ffd91a10bcb.mov

[isaaccorley]

Need to figure out how to get the plotting to run headless within the CI container. That seems to be what's causing tests to fail.

[adamjstewart]

Did you ever open an issue with the developers? Can you link to it here?

[isaaccorley]

A couple things:

• I decided to setup and return the point_cloud PolyData object. Users will be able to run pyvista.plot(point_cloud, ...) themselves to render everything how they see fit. I think this is better because it doesn't assume the other parameters a user wants to define. Let me know if anyone has any objections to this.
• I was able to remove the colormap arg entirely because pyvista.plot supports a cmap arg which effectively does the same thing. So pyvista is already helping clean up the code 👍

Thanks for the assist @banesullivan. I'm really enjoying the simplicity of working with pyvista with point cloud datasets so far!