Change string to unicode in write_transformation
Change string to unicode in write_transformation

This fixes #297.
sunbingfengPI/OpenSFM_Test,sunbingfengPI/OpenSFM_Test,oscarlorentzon/OpenSfM,mapillary/OpenSfM,BrookRoberts/OpenSfM,BrookRoberts/OpenSfM,oscarlorentzon/OpenSfM,sunbingfengPI/OpenSFM_Test,mapillary/OpenSfM,BrookRoberts/OpenSfM,oscarlorentzon/OpenSfM,BrookRoberts/OpenSfM,mapillary/OpenSfM,mapillary/OpenSfM,oscarlorentzon/OpenSfM,sunbingfengPI/OpenSFM_Test,mapillary/OpenSfM,BrookRoberts/OpenSfM,sunbingfengPI/OpenSFM_Test,oscarlorentzon/OpenSfM