Extension branch for Blender 4.2

[vanous]

DO NOT make PRs against this PR or the Extension branch, as most changes should go to main, the extension is then rebased.

This is preparation for the Blender 4.2 extension support and store. The extension support looks pretty good. It allows using wheels, allowing us to move away from vendoring dependencies and having to modify them to use relative imports, then being stuck on old versions.

• [x] Convert everything to relative imports
• [x] Convert imports to not use import *
• [x] Migrate dependencies to wheels
• [x] Migrate Preferences to new structure
• [x] Respect new Internet Access Preferences settings in Blender
• [x] Check and test carefully that everything works
  • [x] sACN
  • [x] OSC
  • [x] Art-Net
  • [x] GDTF
  • [x] MVR
  • [x] MVR-xchange
• [x] Support new user writable storage in 4.2 and up

[vanous]

This is it. New gobo and iris support require Blender 4.2 and up. Extension is the new main, old main is the addon branch.