fat: log more GCP statistics before merge
fat: log more GCP statistics before merge

Summary: ThiS Diff adds a bit more statistics when using GCPs.

Reviewed By: mlopezantequera

Differential Revision: D35185660

fbshipit-source-id: 85b6122c77dee3d531af568a14a7030d60124a10

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