群类型，支持一下类型：

    //member can add quit change group name and portrait, owner can do all the operations
    Normal(0),
    //every member can add quit change group name and portrait, no one can kickoff others
    Free(1),
    //member can only quit, owner can do all the operations
    Restricted(2),
    //member can do nothing, server api manage the group.
    Organization(3);

0 weixin 风格群组;2 QQ 风格群组；这两种群组的主要区别就是群成员所能执行的操作不一样。

群ID，可以自己生成，但要保证唯一。