G-Kanban for Godot 4

[H4x0r-000]

Hi, I made a minimalistic port of G-Kanban for Godot 4. If you want I would create a pull request however since some parts of your addon require Godot features that changed from version 3 to 4, I split my repo into to two branches: godot-3 (same as your main branch) and godot-4 wich is my port. So to properly merge I would recommend that you also split this repo into two branches. For proper separation of the two versions I recommend using the following versioning scheme: 0.1.0g4 (example for version 0.1.0 for Godot 4) / 0.1.0g3 (example for version 0.1.0 for Godot 3)

here is a link to my fork