There is no good solution here, since RNA props can only have one type/unit.
Tried to find the less worse one - have different RNA props for same DNA value
(a bit like the angle/length for camera lens).
Also fixed two other issues with Transform conctraint:
* Angle were still in degrees (yes, another backward-compatibility breacking).
* Scale was absolute, unlike loc/rot.
Also cleaned up a bit the code, replaced some magic numbers by proper enums, ...
8714ae09f8