Complete make-over #6

Update:

• Python 2 to 3
• Conda to poetry
• Add dev tooling (black, ruff, pre-commit)
• VTK to latest (9.2)
• Drop custom VTK build (use vtkMultiVolume)
• PySide to latest (6.5)
• Integrate itk-elastix python package
• Add CI
• Test

Add installers with Pyinstaller:

• Windows
• MacOS
• Build on CI

Or maybe Briefcase?