Differentiate Persians.
- Allows the immortals to be "upgraded" between sword and bow yielding.
- Reduces batch training time per progressing phase.
- Don't kill the immortals partly when reducing their training time.
- More units from the CC.
- Enable the Ice House.
Patch by: @borg-
Differential revision: https://code.wildfiregames.com/D4724
Accepted by: @chrstgtr, @real_tabasco_sauce
Comments by: @marder, @Stan