Re-organisation of folder structure.

[BastiaanOlij]

The template library currently places items in the game folder and img folder. I think this structure needs to change and be brought inline with godot-xr-tools.

I propose the following:

• addons: folder containing the addsons like XR tools itself and the OpenXR plugin/loader
• assets: contains models/images/sounds and other assets
• game: contains the levels of the game, we call this scenes in XR tools
  Need to make a decision which one is more apt
• components: what is currently game/objects
  These should be scenes that are used in multiple levels and/or a collection of useful commonly used items in VR.
  I suggest we move this outside of game so its easier to find once there are many game levels.

[Malcolmnixon]

I agree - separating out the components will help categorizing the template parts a game can optionally reuse from the game parts that should be replaced.