Implement WieldMeshSceneNode which improves wield mesh rendering

- Don't create and cache an extruded mesh for every (non-node) item.
  Instead use a single one per image resolution.

- For cubic nodes reuse a single wield mesh too

- Improve lighting of the wielded item

- Increase far value of wield mesh scene camera, fixes #1770

- Also includes some minor refactorings of Camera and GenericCAO.

src/player.h

@@ -249,8 +249,6 @@ public:
 	bool swimming_vertical;
 	bool camera_barely_in_ceiling;
 	
-	u8 light;
-
 	Inventory inventory;
 
 	f32 movement_acceleration_default;