Blender Git Loki

Object tracking integration

This commits merges object tracking implementation from tomato branch.

Summarized changes from branch:

- Added list of objects to be tracked. Default there's only one object called
"Camera" which is used for solving camera motion. Other objects can be added
and each of them will have it;s own list of tracks. Only one object can be used
for camera solving at this moment.
- Added new constraint called "Object Tracking" which makes oriented object be
moving in the save way as solved object motion.
- Scene orientation tools can be used for orienting object to bundles.
- Object has got scale to define "depth" in camera space.
- All tools which works with list of tracks or reconstruction data now
gets that lists from active editing object.
- All objects and their tracking data are available via python api.
- Improvements in witness cameras workflow,