Name space views after the space and indicate duplicate names

[jleibs]

Resolves: #1220

Consider this (admittedly silly) code:

import rerun as rr
import numpy as np

rr.init("space_test", spawn=True)
rr.log_points("space_a/points", positions=np.random.rand(10, 3))
rr.log_points("space_b/space_a/points", positions=np.random.rand(10, 3))
rr.log_points("space_c/points", positions=np.random.rand(10, 3))
rr.log_unknown_transform("space_b/space_a")

Before:

After:

Additionally hitting "clone view" now generally does the right thing.

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[emilk]

With this PR we now sometimes get more things named after root (/):

…but I still think that this PR is an improvement.

But it would be good to add a comment here for why this is the better choice, so we don't regress here.