Make COR conversion from rel to abs consistent throughout the software

The conversion from relative COR (output of CORFinder.find_cor()) to absolute position in not consistent depending of the COR estimator. In CORFinder SinoCORFinder, the conversion is abs = rel + detector_width // 2. In CompositeCORFinder, the conversion is abs = rel + (detector_width - 1)// 2. After discussion with @paleo, it seems that the second one is the right one (to be confirmed).

Note that tomwer converts CompositeCORFinder does (see #1136). Consistency should be enforced through the tomotools.