[FIX] Force LUT to be RGB

[skoudoro]

This PR is due to some change on the alpha channel with VTK9.
The event on the actor is not called if we do not force the LUT to be RGB. This is a quick fix for DIPY Horizon but we need to go deeper in our custom interactor.

See the code below to reproduce the error:

from fury import actor, window
import numpy as np

# It is working with this array
# arr = np.random.rand(375).reshape((5, 5, 5, 3)) * 255
# ERROR with the array below
arr = np.random.rand(125).reshape((5, 5, 5)) * 255

def left_click_callback(obj, ev):
    print('CALLBACK')
    print(obj)

fig = actor.slicer(arr)
fig1 = fig.copy()
fig1.display(None, None, 0)
print(fig1.shape)
fig1.SetInterpolate(False)
fig1.AddObserver('UserEvent',
                 left_click_callback, 10000.0)
scene = window.Scene()
showm = window.ShowManager(scene, interactor_style='custom')
showm.initialize()
scene.add(fig1)
showm.start()

[codecov]

Codecov Report

Merging #329 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #329   +/-   ##
=======================================
  Coverage   88.65%   88.65%           
=======================================
  Files          21       21           
  Lines        5075     5076    +1     
  Branches      656      656           
=======================================
+ Hits         4499     4500    +1     
  Misses        406      406           
  Partials      170      170           

Impacted Files	Coverage Δ
fury/window.py	78.42% <ø> (ø)
fury/actor.py	92.84% <100.00%> (+<0.01%)	⬆️