Terraform unique triggerable from improvements

By SomeTroglodyte:
- Right-click/longpress for World screen city buttons
- Fix some uses of "hidden from users" modifer
- Fix fortified units upgraded to unfortifyable ones keeping fortification
- Empire Overview Screen closing now with same UX as Civilopedia

Added unit escorting formation!  - By tuvus

Allow conditional timed triggers for unit actions &c  - By SeventhM

Allow Barbarians to make set-up ranged units  - By SpacedOutChicken