[Gameplay A24] - Introduce two new technologies at the stable.

Now the stable is available for all civs (r24470 / rP24470) new techs for it are welcome.
This introduces:

• town-phase technology that gives cavalry +10% health;
• city-phase technology that gives the stable -0.1 corral batch training time (similar to the one the barracks has).

The two Persian levy technologies, which used to give -20% training time and -5% health, now simply grant -10% training time instead.

Patch by: @Nescio
Differential revision: D3317
Reviewed by: @borg-