function getOrphanedLists () {
	if (!this.nav) {
		return [];
	}
	return _.filter(this.lists, function (list, key) {
		if (list.get('hidden')) return false;
		return (!this.nav.by.list[key]) ? list : false;
	}.bind(this));
}
Retrieves orphaned lists (those not in a nav section)