Made python scripts runnable directly on Linux.

Added execute bit and shebang line to start the python3 interpreter.

spacevoxelviewer.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import numpy as np
 import matplotlib.pyplot as plt
 from astropy.io import fits  # For reading FITS files

voxelmotionviewer.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 """
 pyvista_interactive_view_with_rotation_history.py