Make sure team is consistently set to -1 on connection for human players and bots

Make sure team is consistently set to -1 on connection for human players and bots

Thanks to this change
* the Player_ChangeTeam and Player_ChangedTeam mutator hooks (currently unused by any
  mutator / gamemode) are consistently no longer called on connection
* the workaround in Player_SetTeamIndex that handles the situation where a bot unintentionally spawns
  with a valid team set depending on its personal colors is no longer needed