Add option to unrank

[Garanas]

The back-end version of FAForever/fa#3440. I'll add details about the option here as it gets more defined.

[Garanas]

Example of the game options when it is set to unrank / unrated ('Yes').

{
   AIBuilderNameDebug="off",
   AIDebugDisplay="displayOff",
   AIEndlessGameLoop="off",
   AIMapMarker="miss",
   AIOverwhelmDelay=20,
   AIOverwhelmIncrease=0.025000000372529,
   AIPLatoonNameDebug="off",
   AIPathingDebug="off",
   AIReplacement="Off",
   AIThreatDisplay="threatOff",
   AIUnitCap="0",
   AllowObservers=true,
   AutoTeams="tvsb",
   BuildMult="2.0",
   CheatMult="2.0",
   CheatsEnabled="true",
   CivilianAlliance="enemy",
   DelayUntilNextWave="50",
   DmgBonus="0.4",
   FogOfWar="none",
   GameSpeed="adjustable",
   HPBonus="4",
   HoldTime="40",
   LandExpansionsAllowed="5",
   MainBuildingHP="100",
   MySpecialKey1="off",
   NavalExpansionsAllowed="4",
   NoRushOption="Off",
   OmniCheat="on",
   PrebuiltUnits="Off",
   RandomMap="Off",
   RevealCivilians="No",
   ScenarioFile="/maps/adaptive_moon.v0002/adaptive_moon_scenario.lua",
   Score="yes",
   Share="FullShare",
   ShareUnitCap="allies",
   TMLRandom="0",
   TeamLock="locked",
   TeamSpawn="fixed",
   Timeouts="-1",
   UnitCap="1000",
   Unranked="Yes",      -- <- this value
   Victory="sandbox",
   WavesStartTime="600"
}

And a smaller example when it is set to ranked / rated ('No'):

{
    -- (...)
    UnitCap="1000",
    Unranked="No",
    Victory="sandbox",
    -- (...)
}

The option defaults to 'No' e.g., do not unrank - if the option is not set all together the game should therefore be ranked.