Cycles: Initial implementation of detailed statistics

Gathers information about object geometry and textures. Very basic at
this moment, but need to start somewhere.

Things which needs to be included still:

- "Runtime" information, like BVH. While it is not directly controllable
  by artists, it's still important to know.

- Device array sizes. Again, not under artists control, but is added to
  the overall size.

- Memory peak at different synchronization stages.

At this point it simply prints info to the stdout after F12 is done,
need better control over that too.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D3566

intern/cycles/render/scene.cpp

@@ -379,4 +379,10 @@ void Scene::device_free()
 	free_memory(false);
 }
 
+void Scene::collect_statistics(RenderStats *stats)
+{
+	mesh_manager->collect_statistics(this, stats);
+	image_manager->collect_statistics(stats);
+}
+
 CCL_NAMESPACE_END