Blender Git Loki

Tweaks and improvements to fundamental/homography estimation

- A bit more reasonable name for the estimation option
structure and estimation functions.

- Get rid of unclear function and parameter tolerance,
it wasn't clear at all in which units they are.

Now we've got expected_average_symmetric_distance as
an early output check and as soon as average symmetric
error goes below this threshold refining finishes.

This distance is measured in the same units as input
points are.

It is arguable whether we need callback for this or not,
but seems Ceres doesn't have some kind of absolute
threshold for function value and function_tolerance
behaves different from logic behind expected symmetric
error.

- Added option to normalize correspondences before
estimating the homography in order to increase estimation
stability. See

R. Hartley and A. Zisserman. Multiple View Geometry in Computer
Vision. Cambridge University Press, second edition, 2003.

https://www.cs.ubc.ca/grads/resources/thesis/May09/Dubrofsky_Elan.pdf