Layers: Separate between scene render layer (F12) and context render layer (everything else)

For now they are the same. However with workspaces they will be
different, and should be treated differently.

source/blender/blenkernel/intern/context.c

@@ -906,7 +906,7 @@ SceneLayer *CTX_data_scene_layer(const bContext *C)
 		return sl;
 	}
 	else {
-		return BKE_scene_layer_active(CTX_data_scene(C));
+		return BKE_scene_layer_context_active(CTX_data_scene(C));
 	}
 }