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, ...
Bevel Factor Mapping allows to control the relation between bevel factors
(number between 0 and 1) and the rendered start and end point of a beveled
spline.
There are three options: "Resolution", "Segments", "Spline". "Resolution"
option maps bevel factors as it was done < 2.71, "Spline" and "Segments"
are new.
* "Resolution“: Map the bevel factor to the number of subdivisions of a
spline (U resolution).
* "Segments“: Map the bevel factor to the length of a segment and to the
number of subdivisions of a segment.
* "Spline": Map the bevel factor to the length of a spline.
Reviewers: yakca, sergey, campbellbarton
CC: sanne
Differential Revision: https://developer.blender.org/D294
