volumina.api: Don't auto-import 3D widgets with volumina.api so that the volumina.NO3D flag is respected.
tiling.py:
- Worker threads have unique names
- Don't print exceptions to stderr (assume that sys.excepthook will do the right thing)
tiling: Attempt to kill all worker threads at app exit (hopefully this avoids some exceptions during interpreter shutdown)
Replaced some print statements with logging statements.