toDo: Possible improvements to viz scripts

[EmmaRenauld]

As per Alex's comments in reviews from PR #1137 , here are possible improvements to be done in viz scripts:

• viz.gradients.plot_each_shell and viz.gradients.plot_proj_shell should use create_interactive_window from viz/backends/fury if interaction is required. If titles are needed on the silent output, they should be drawn using annotations.

• In scil_viz_tractogram_seeds_3d.py, if --silent option is used, a screenshot could be saved on disk, using (snapshot_scenes + compose_image). It could also use create_interactive_window from viz/backends/fury

[EmmaRenauld]

viz_bundle_screenshot_mni: no coverage.

When running:

scil_viz_bundle_screenshot_mni.py:292: UserWarning: We'll no longer accept the way you call the display function in future versions of FURY.
Here's how to call the Function display: display(self_value, x='value', y='value', z='value')
  display_slices(volume_actor, slices_choice,