Differentiate Sparta.
This differentiates Sparta by giving them P1 champions, a Hero-oriented team bonus and a new unit.
Sparta should rely heavily on their extremely powerful melee infantry, hence the focus is on that with choice and upgrade.
Patch by: @borg-
Differential revision: https://code.wildfiregames.com/D4736
Accepted by: @chrstgtr, @real_tabasco_sauce
Comments by: @Langbart, @marder, @wowgetoffyourcellphone