Differentiate Athenians.
This gives them a new hero (Hippocrates; recruitable from the tempel) and some unique Naval bonuses.
Patch by: @borg-
Differential revision: https://code.wildfiregames.com/D3727
Accepted by: @real_tabasco_sauce
Comments by: @chrstgtr, @ValihrAnt, @wowgetoffyourcellphone