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/localplayer.h

@@ -71,6 +71,8 @@ public:
 	std::string hotbar_image;
 	std::string hotbar_selected_image;
 
+	video::SColor light_color;
+
 	GenericCAO* getCAO() const {
 		return m_cao;
 	}