AI tweaks for better targeting

Cannot alter city build queue in between turns

Fixed 'destroy civilian unit before attack' crash

Terrain-Specific Natural Wonder Sprite Support  - By OptimizedForDensity

By vegeta1k95:
- City Screen improvements
- Fix crash when attacking city with disabled overlays
- PolicyScreen: branch progress + fix spectator

Trade button initially disabled - By lishaoxia1985

By Gualdimar:
- Collapsible tutorial tasks
- Bigger header on policy and mod screens