(a) A partnership agreement may provide for classes or groups of general partners having such relative rights, powers and duties as the partnership agreement may provide, and may make provision for the future creation in the manner provided in the partnership agreement of additional classes or groups of general partners having such relative rights, powers and duties as may from time to time be established, including rights, powers and duties senior to existing classes and groups of general partners. A partnership agreement may provide for the taking of an action, including the amendment of the partnership agreement, without the vote or approval of any general partner or class or group of general partners, including an action to create under the provisions of the partnership agreement a class or group of partnership interests that was not previously outstanding.