Update visible cell selection

[banesullivan]

this provides some updates to fix visible cell selection when multiple meshes are in a scene.

Relevant to #560

Example

import pyvista as pv

centers = [(0, 0, 0), (1, 0, 0), (-1, 0, 0),
           (0, 1, 0), (0, -1, 0)]
radii = [1, 0.5, 0.5, 0.5, 0.5]

spheres = pv.MultiBlock()
for i, c in enumerate(centers):
    spheres.append(pv.Sphere(center=c, radius=radii[i]))

p = pv.Plotter(notebook=False)
p.add_mesh(spheres)
p.enable_cell_picking(through=False)
p.show()

Previous behavior:

New behavior: