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/util/numeric.h

@@ -361,5 +361,10 @@ inline float cycle_shift(float value, float by = 0, float max = 1)
     return value + by;
 }
 
+inline bool is_power_of_two(u32 n)
+{
+	return n != 0 && (n & (n-1)) == 0;
+}
+
 #endif