Remove building-improvement if the building is no longer buildable

By RobLoach:
- Add 'when not stacked with a [mapUnitFilter] unit' Conditional 
- Fix relevent Civ for within tiles Conditional 
- City Screen: Display Stockpile Amount Available for Cost 

Display promises in diplomacy overview for human players - By unciv-loof

Fix battle notification translations - by dadadnet (new contributor!)