r22: restore coordinate transforms for rectangular detectors

• Clean up the RectangularDetector API. Get rid of the setDetector* and setPerpendicular* functions. Set everything in the constructor. Since makes the constructor too complicated for direct use, we will in the future call dedicated factory functions, similar to the way we construct Scale instances using functions from MakeScale. - done in !1859 (merged)
• In branch coord, add a map to class Scale that holds lambda functions, indexed by target dimension, that provide transforms. - done in !1874 (merged)
• In the RectangularDetector c'tor, set all available transforms. - done in !1874 (merged)
• Repair example AxesInDifferentUnits. - done in !1874 (merged)