Denotation official of CDs

[kohlhase]

see OpenMath/OM3#7

[kohlhase]

The discussion under OpenMath/OM3#7 basically agreed that the status official is overly proprietary and should be replaced.

There is also a related discussion at OpenMath/OpenMath.github.io#47 which discusses James' new idea of having categories supported/contributed/external. Note that these are not thought of as new CDStatus values, but for collections.

With these new names, it strikes me that the statuses Official and Experimental belong to different dimensions, and have been bad choices in any case. How about if we introduce the CDStatus Stable as a synonym for Official and deprecate the latter. That way this update would be small enough for OM2r2.

Moreover, if we can get s/c/e to pull some weight (e.g. by integrating them more tightly into the web site), then the aspect "supported by the OpenMathSoc" which was conveyed by Official would be taken over by that mechanism.