Test necessity for camera calibration

[LukasBommes]

Currently, the docs recommend calibrating the camera.
We should test the possibility of simply computing the focal length based on the lens datasheet, setting the image center to zero and assuming zero distortion. Since OpenSfM optimizes calibration parameters during the reconstruction it could be possible that accurate parameters are obtained without prior manual calibration. Concern is a decrease of the robustness of the OpenSfM reconstruction when starting from sub-optimal camera parameters.