Reconstructed scene scale ambiguity improvement

Made it so reconstructed scene always scaled in a way
that variance of camera centers is unity.

This solves "issues" when different keyframes will
give the same reprojection error but will give scenes
with different.scale, which could easily have been
considered as a bad keyframe combination.

This change is essential for automatic keyframe
selection algorithm to work reliable for user.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56632 954f8c5b-7b00-dc11-b283-0030488c597c
Made bundles in 3D viewport have constant size

This means bundles' size is not affected by camera scale.
This way it's more useful to work with -- bundles never
becomes too small or too large (depending on reconstructed
scene scale).

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56633 954f8c5b-7b00-dc11-b283-0030488c597c
Setting tracking object scale shall not depend on active object

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56634 954f8c5b-7b00-dc11-b283-0030488c597c
Added a button to apply scale on scene solution

This is an alternative to using camera to scale the
scene and it's expected to be better solution because
scaling camera leads to issues with z-buffer.

Found the whole scaling thing a bit confusing,
especially for object tracking, but cleaning this up
is a bit different topic.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56635 954f8c5b-7b00-dc11-b283-0030488c597c
Add check for points behind camera in euclidan BA cost functor

In cases keyframes are no so good, algebraic two frames construction
could produce result, for which more aggressive Ceres-based BA code
will fall to a solution for which points goes behind the camera,
which is not so nice.

Seems in newer Ceres returning false from cost functor wouldn't
abort solution, but will restrict solver from moving points behind
the camera.

Works fine in own tests, but requires more tests.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56636 954f8c5b-7b00-dc11-b283-0030488c597c