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/mapblock_mesh.h

@@ -195,6 +195,11 @@ u16 getInteriorLight(MapNode n, s32 increment, INodeDefManager *ndef);
 u16 getFaceLight(MapNode n, MapNode n2, v3s16 face_dir, INodeDefManager *ndef);
 u16 getSmoothLight(v3s16 p, v3s16 corner, MeshMakeData *data);
 
+// Converts from day + night color values (0..255)
+// and a given daynight_ratio to the final SColor shown on screen.
+void finalColorBlend(video::SColor& result,
+		u8 day, u8 night, u32 daynight_ratio);
+
 // Retrieves the TileSpec of a face of a node
 // Adds MATERIAL_FLAG_CRACK if the node is cracked
 TileSpec getNodeTileN(MapNode mn, v3s16 p, u8 tileindex, MeshMakeData *data);