Unit triggerables with triggers, no longer trigger on new units

Clicking on statuses opens promotion screen

AI: 
- City states disband great prophets
- Don't offer peace when we're just about to take a city

Multiplayer:
- Better, less buggy resign/skip

Modding:
- Fix global unique validation
- Validation catches 'global triggers attached to unit triggerables', which will have no effect

By SomeTroglodyte:
- Fix Resources Overview to work as intended 
- Add an 'XP' column to Units Overview