Update URDF Importer to process sensor elements.

Update the URDF Importer to add sensors as 0 mass 0 inertia elements
attached by a fixed joint. This way their states can be read as links.

examples/SharedMemory/SharedMemoryPublic.h

@@ -820,6 +820,7 @@ enum eURDF_Flags
 	URDF_ENABLE_SLEEPING = 2048,
 	URDF_INITIALIZE_SAT_FEATURES = 4096,
 	URDF_USE_SELF_COLLISION_INCLUDE_PARENT = 8192,
+  URDF_PARSE_SENSORS = 16384,
 };
 
 enum eUrdfGeomTypes  //sync with UrdfParser UrdfGeomTypes