public void QuitFromConversation(long conversationId)
{
var conversation = AttendedConversations.Where(x => x.Id == conversationId).FirstOrDefault();
var attendee = conversation.Attendees.Where(x => x.UserAccount.Id == UserAccount.Id).FirstOrDefault();
conversation.Attendees.Remove(attendee);
AttendedConversations.Remove(conversation);
conversation.NotifyConversationUsers(UserAccount.UserName + " has quitted from conversation. " + DateTime.Now.ToShortDateString());
}
