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.cpp

@@ -39,7 +39,6 @@ Player::Player(IGameDef *gamedef, const char *name):
 	is_climbing(false),
 	swimming_vertical(false),
 	camera_barely_in_ceiling(false),
-	light(0),
 	inventory(gamedef->idef()),
 	hp(PLAYER_MAX_HP),
 	hurt_tilt_timer(0),