Document in coos.ttl the classification rule for OverarchingActivity #113

The description of GAMSO reads as follow:

In addition, COOS defines the OverarchingActivity class, which represents a supporting activity that applies to all production phases, e.g. metadata management, data management, statistical methodology management, etc. These activities correspond to the overarching processes in the GSBPM and the statistical activities in Corporate Support in GAMSO

I interpret this as the following formal rule : _"Any coos:Activity whose dcterms:type is an entry that is a narrower concept of GAMSO activityArea/3 (Corporate Support), or whose dcterms:type is GSBPM overarchingActivity/0.1, overarchingActivity/0.2 or overarchingActivity/0.3 is of type OverarchingActivity".

While this would be complicated to formally encode this in OWL, I suggest that rule is made explicit in the definition of the OverarchingActivity class, to clearly define the relationship between the SKOS "loose typing" part of COOS, and the OWL "strong typing".