Broken feat.: f.scatters = [] or del(f.scatters[i])

[TimoFriedri]

Version 0.6.0.a4

Example:

f = ipv.figure()
s = ipv.scatter(*np.random.random([3,10]))
ipv.show()
f.scatters = []
s2 = ipv.scatter(*np.random.random([3,10]), color="blue")
s3 = ipv.scatter(*np.random.random([3,10]), color="green")
del(f.scatters[0])

The scatters will not be removed from the figure!

Looking at the figure.ts file, this should definitely be the case.
updates_scatters() has a remove_from_scene() call, but nothing happens.

Furthermore I think the logic is incorrect for an empty scatters list.
There is only this line [1440] this.scatter_views = {}; but shouldn't there be also the call of remove_from_scene() for each scatter_view beforehand if scatter_views wasn't empty?