CURA-12660
The UV-unwrapping is now done in a background job, and the UI displays a waiting state. This fixes the issue where the user would start painting but the model was not ready yet, and the first stroke would be missing.
Should be able to paint pixels now if the tools is active, and the model loaded is with UV-coords (that rules out our current impl. of 3MF at the moment -- use OBJ instead), and you position the model outside of the build-plate so the paint-shadr that is temporarily replacing the 'disabled' one is showing.
Will need a lot of extra features and optimizations still!
part of CURA-12543
