Provide standard background loading scene

[Malcolmnixon]

Projects would benefit from a standard loading scene similar to the staging scene in the demo project.

[BastiaanOlij]

I'm going to find some time for this soon as discussed on stream. There are two parts to this:

• The staging scene should move into our tools library and then an inherited scene added to the demo so users who wish to create a multi level game can use our entire setup.
• The loading screen node should become a Spatial in out base staging scene with the actual sub scene moving underneath in our inherited scene. The scene should get a base scene that is added to our tools library with the current version being an inherited scene for our demo.

The idea here is to make it easier for people to create more complex games however in a way that is completely optional.

[BastiaanOlij]

Implemented with #201