Adds a lower cap for latejoing antagonists

-If the number of antagonists is 2 less than the current cap, the next latejoiner will be guaranteed to get antagonist
-Reduced latejoin antag cap to (Number of joined players/ Scaling Coefficient)

This should result in a more controlled population of antagonists while still keeping it unpredictable for players in-game.
Merge pull request #4035 from Ikarrus/latejoinfloorcap

Adds a floor cap for latejoing antagonists