Add 3D datasets about pyntcloud HOT 3 OPEN

Hi, David.
There are lots of dataset in the area of points cloud, such as:
http://modelnet.cs.princeton.edu

There might be a few glitches in the original raw data files, but it can be relived easily with _fix_offfile() in here

btw, I do notice that during the random sampling using the random sampler from pyntcloud on this dataset, it some time encounter with the overflow in the multiplication, so I has set the data storage as 64 bit instead of 32 bit by default. And this problem is resolved :)

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Hola @hansen7 ! Have you checked the existing modelnet downloader?:

https://github.com/daavoo/pyntcloud/blob/master/pyntcloud/learn/datasets/modelnet.py

I did not encounter this overflow issues. Will try to look into that

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I'm not 100% sure that this is a float64/32 issue

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