[Bf-codereview] Operator to setup scene for camera tracking (issue 5432048)

[sergey.vfx at gmail.com]

Reviewers: bf-codereview_blender.org,

Description:
This patch implements button called "Setup Tracking Scene". This button
makes the following:
- Sets background to 3d viewports
- Makes camera be following solved camera (adds Camera Sovle constraint)
- Set ups render layers (foreground and background)
- Places sample objects into scene
- Makes nodes setup

Probably it can be cleaned up or simplified/optimized in some places.

P.S. There are some small improvements planned, but they aren't large
and prefer to start reviewing patch sooner.

Please review this at http://codereview.appspot.com/5432048/

Affected files:
   release/scripts/startup/bl_operators/clip.py
   release/scripts/startup/bl_ui/space_clip.py