Camera tracking: operator to setup scene for compositing things into footage

This operator does needed changes to

- 3D viewport
- Scene settings
- World settings
- Compositor
- Scene objects

in a way scene becomes ready to be composited into footage.

Known issue: preview doesn't work "out-of-box" after running this script,
selecting View node and hitting Tab helps. Not sure it can be solved
in nicer way at this moment.

release/scripts/startup/bl_ui/space_clip.py

@@ -640,6 +640,7 @@ class CLIP_PT_tools_clip(Panel):
         layout = self.layout
 
         layout.operator("clip.set_viewport_background")
+        layout.operator("clip.setup_tracking_scene")
 
 
 class CLIP_MT_view(Menu):