Mafia: Fix bugs, killmsg, haxMultiplier

Fix startup.revealPlayersMsg sending even when no player is being revealed.
Fix watchFirst, lynch.killVoters.first and lynch.convertVoters.first defaulting to 1 even when set to 0.
Added Action.killmsg, which overrides theme's killmsg for that action.
Added haxMultiplier, which affect hax rate on a per command basis.
Update mafiachecker.js
Merge pull request #735 from IceKirby/patch-27

Mafia: Fix bugs, killmsg, haxMultiplier