Added the shutdown call after exec finishes. This frees up the single…

…ton class for the next initialization

src/tcviewer/mol_widget.py

@@ -377,7 +377,7 @@ def __init__(self):
         self.renWin.AddRenderer(self._base_ren)
 
         self.Initialize()
-        self.Start()
+        # self.Start()
 
         self._recording_mouse = False
         self._mouse_pos = None

src/tcviewer/screen.py

@@ -96,6 +96,7 @@ def __enter__(self):
         def __exit__(self, *args):
             self.window.show()
             self.exec()
+            self.shutdown()
 
         def draw_molecule(self, *args, **kwargs):
             self.molview.draw_molecule(*args, **kwargs)