Improved Antagonist Scaling

To allow for saner antagonist scaling at high-population while still accomodating low-population rounds.

The PR changes the formula to thus:
Antagonists = min ( population / (2* coeff ) + 2, population / coeff )

For traitor, this means
Traitors = min ( population / 10 + 2, population / 5 )
Actually, let's keep the coeffs as is
Merge pull request #4657 from Ikarrus/betterantagscaling

Improved Antagonist Scaling