(NC-140) Each group has a rule, each rule a group.

Rather than the previous many:many relationship between rules and groups, each rule is now tightly linked 1:1 with a group, and is not a seperate entity as far as the API is concerned. This is not a loss of power since each rule can be an arbitrary boolean expression on facts.

Since rules are not seperate entities, they are now expected to be supplied when creating a group, are returned in their group's JSON representation, and can be updated by updating the group with a delta.