Make stub generation repeatable and less memory hungry

[friedererdmann]

Optimize stub generation by cleaning the scene before and after the generation of the stubs. Investigate if turning off UI/Viewport elements can improve generation speed as well. Provide visual feedback how far along the stub generation is.

[friedererdmann]

Already decreased memory and time by moving from creating a new object per property to analyzing all properties of one class from the same object in 85a161c. Still need to make repeatable.