Always require lobby authentication for lobby matches, refs #3549 / rP21520 / D897.

This is due to too many oversteppings of the lobby Terms of Use following JS mods that implemented an UI for players to join lobby games with arbitrary nicknames or 'replace' / impersonate other players in lobby games.

Agreed with: user1, Dunedan
Code proofread by: Vladislav
Minor discussions with: Imarok, Hannibal_Barca, smiley, fpre, bb, nani
refs https://wildfiregames.com/forum/index.php?/topic/24722-improving-mod-security/