- Slicing bugfix.

- Sort imports.
- Make sitk-elastix optional again.

tests/test_open.py

@@ -1,7 +1,8 @@
 import pickle
-import pytest
-from pathlib import Path
 from multiprocessing import active_children
+from pathlib import Path
+
+import pytest
 from ndbioimage import Imread, ReaderNotFoundError