activitymanager: add counts/scores helpers

Signed-off-by: Imre Deak <imre.deak@intel.com>
party: add activity count/score helpers
api: factor out MemberResource.get_member
api: add activity scores to the member resource
api: add activity scores to the party resource

Signed-off-by: Imre Deak <imre.deak@intel.com>