[Gameplay] Han - adjust crossbow stats & training techs

Similar dps as a slinger now, but with higher repat time. Normal citizen soilder cost.
Nerf the crossbow training technology a bit.
Make the archer & crossbow technology availabe in the stable as well, as it they also affect cavalry units.

accepted by : @real_tabasco_sauce
positive comment from: @borg-

Differential revision: https://code.wildfiregames.com/D4721