Fix oversights in recent commits.
- Sounds of macemen (r24499 / rP24499, r24478 / rP24478).
- Kushite healer start unit on (most) skirmish maps (r24422 / rP24422).
- Fortress tooltips (r24393 / rP24393 and r24470 / rP24470).
- Rome siege wall foundations (r23609 / rP23609).
- Removed IshtarGate visible class.
- Move Ishtar Gate of Babylon from Persians (it is Neo-Babylonian) (r23888 / rP23888).
- Rename barracks.png -> military.png (r24470 / rP24470) and ishtar_gate.png -> bull.png icons (refs D2551).
- Insert placeholder icons for free and autoresearched technologies (D3262#145001).
- Update balancing credits (r24496 / rP24496).
Patch by: @Nesio
Differential revision: D3292