Refactoring v1.0 prep

This is the first big refactoring step towards v1.0 Lots of functions changed places and names, so there are probably lots of bugs to correct now.

qim3d/processing/__init__.py

-from .local_thickness_ import local_thickness
-from .structure_tensor_ import structure_tensor
-from .detection import blob_detection
-from .filters import *
-from .operations import *
-from .cc import get_3d_cc
-from .layers2d import segment_layers, get_lines
-from .mesh import create_mesh
-from .features import volume, area, sphericity
+from ._local_thickness import local_thickness
+from ._structure_tensor import structure_tensor
+from ._layers import segment_layers, get_lines