Group starting positions of players by team on the new random map sripts in Alpha 20 and 21, making them much more playable.
Use stronghold starting position style with 33% instead of 50% probability.

Differential Revision: https://code.wildfiregames.com/D664
Reviewed but not accepted by: bb (everything) and fatherbushido (Heaps permutations)
Catch: This must become more efficient if the playercount will be greater than 8, refs #4004.