Structure tensor wrapper

In addition to the wrapper and viz function, I also black formatted some of the my previous merges as I had forgot it. Also increased the width of the local thickness slice index slider to be coherent with the ones in the structure tensor viz function

qim3d/processing/__init__.py

 from .filters import *
-from .local_thickness import local_thickness
\ No newline at end of file
+from .local_thickness import local_thickness
+from .structure_tensor import structure_tensor
\ No newline at end of file