Moved the Activity class from va-spec core-im into gkscommon (because Contribution inherits from this class). Made a couple minor updates to property descriptions here.
Updated Contribution to reference/extend Activity as needed
state its inheritance from Activity
define contributor to extend performedBy, so we can give a more precise definition and constrain cardinality to one Agent
removed contirbutionMadeTo property - there is no real use case for it, as Contributions are always referenced from the artifacts contributed to, not the other way. And this avoids us needing to move InformationEntity into gks-common.
removed date, as this property is now inherited from Activity.
changed name of activity -> activityType, to be clear that what goes here is a code representing the type of activity performed in making the contribution. For now, only one type allowed per contribution, but we may want to allow for an array here in the future.
contributorto extendperformedBy, so we can give a more precise definition and constrain cardinality to one AgentcontirbutionMadeToproperty - there is no real use case for it, as Contributions are always referenced from the artifacts contributed to, not the other way. And this avoids us needing to move InformationEntity into gks-common.date, as this property is now inherited from Activity.activity->activityType, to be clear that what goes here is a code representing the type of activity performed in making the contribution. For now, only one type allowed per contribution, but we may want to allow for an array here in the future.