Allow using a different set of ignore values when computing depthmaps
Allow using a different set of ignore values when computing depthmaps

Summary:
So far, segmentation_ignore_values are used both for SfM (feature extraction and matching) and MVS (depthmap computation).

This enables specifying a different set of values for each step. The behavior defaults to the previous one if the undistorted_segmentation_ignore_values are not specified.

Reviewed By: arknapit

Differential Revision: D30867189

fbshipit-source-id: e800302f781c1fb6498d1defe05eca0248ee0234

mapillary/OpenSfM,mapillary/OpenSfM,mapillary/OpenSfM,mapillary/OpenSfM,mapillary/OpenSfM