refactor: functions to set and get BA cameras
refactor: functions to set and get BA cameras

sunbingfengPI/OpenSFM_Test,oscarlorentzon/OpenSfM,mapillary/OpenSfM,sunbingfengPI/OpenSFM_Test,mapillary/OpenSfM,oscarlorentzon/OpenSfM,mapillary/OpenSfM,oscarlorentzon/OpenSfM,BrookRoberts/OpenSfM,oscarlorentzon/OpenSfM,mapillary/OpenSfM,sunbingfengPI/OpenSFM_Test,oscarlorentzon/OpenSfM,BrookRoberts/OpenSfM,BrookRoberts/OpenSfM,sunbingfengPI/OpenSFM_Test,BrookRoberts/OpenSfM,mapillary/OpenSfM,sunbingfengPI/OpenSFM_Test,BrookRoberts/OpenSfM