Blender Git Loki

Camera tracking: expose progress and status from camera solver into interface

Reporting progress isn't really accurate, but trying to make it more linear
can lead to spending more effort on it than having benefit. Also, changing
status in the information line helps to understand that blender isn't hang
up and solving is till working nicely.

Main changes in code:
- libmv_solveReconstruction now accepts additional parameters:

* progress_update_callback - a function which is getting called
from solver algorithm to report progress back to Blender.
* callback_customdata - a user-defined context which is passing
to progress_update_callback so progress can be updated in needed
blender-side data structures.

This parameters are optional.

- Added structure MovieTrackingStats which is placed in MovieTracking
structure. It's supposed to be used for displaying information about
different operations (currently it's only camera solver, but can be
easily used for something else in the future) in clip editor.
This statistics structure is getting allocated for time operator is
working and not saving into .blend file.

- Clip Editor now displays statistics stored in MovieTrackingStats structure
like it's done for rendering.