Add the draw_plotly method and a tutorial notebook

[FromBei-JingWithLove]

draw_plotly method: visualize 3D models using plotly so that we can directly see models in cloud notebooks.

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[FromBei-JingWithLove]

Reviewed 2 of 4 files at r1, 3 of 3 files at r3, all commit messages. Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @FromBei-JingWithLove and @yxlao)

python/open3d/visualization/draw.py line 35 at r3 (raw file):

import open3d as o3d
import numpy as np
import plotly.graph_objects as go

Are all these import necessary? They don't get used in draw.py.

No. I added the draw_plotly method in draw.py so I added the imports. I will delete them and make a new commit.