'Groups the activities based on their group
Found by running get_group(actvity on them)'

def group_activities(self, activities):

    aggregate_dict = dict()
    activities = list(activities)
    activities.sort()
    for activity in activities:
        group = self.get_group(activity)
        if (group not in aggregate_dict):
            aggregate_dict[group] = self.aggregated_activity_class(group)
        aggregate_dict[group].append(activity)
    return aggregate_dict
