GamesHandler: Allow unassisted player substitution by NickServ account match

[FastLizard4]

Currently, a player may only use ?substitute to sub-in for another instance of themselves if there's an exact user@host match. However, sometimes these change even for the same person, so if there's no match there should also be a check by NickServ account. Since some IRC networks don't support WHOX (including LizardIRC), this will require implementation of some dirty WHOIS command usage for networks without WHOX suport.

Note: First version of Secret Hitler (and GamesHandler) is currently feature-frozen and held for final revisions, bug fixes, and code review before publishing. This issue is deferred until after this first version is code reviewed and published. See #22 and #20.