add calibration file for 1280x720 px images, derived from the calibration for 1920x1080 px images

Hawo and me found out that the incorrect 3D poses of the detected markers, in case of using replayed images, are due to a resolution mismatch of what the Armar6 stereo camera calibration file assumes and what the default image recorder on Armar6 provides. Using a dedicated calibration file for a 720p image resolution fixes the transformation.

This merge request provides that calibration as an additional file.