Add notification handlers for `notify_delete_talk/talker`

[yotsuya]

This PR adds notification handlers for the following notifications.

• notify_delete_talk

  • This notification is sent when the logged-in user exits the talk room.
  • Handler TODO:
    • [x] Close Channel created on the exited talk room.
    • [x] Remove TalkRoom from clientTalkRooms of Client.

• notify_delete_talker

  • This notification is sent when the other user exits the talk room.
  • Handler TODO:
    • [x] Close Channel which has no participants as a result of the user exiting.
    • [x] Remove UserId of the exited user from talkUserIds of TalkRoom.

[igrep]