New unique trigger: "<upon expending a [mapUnitFilter] unit>"

Console:
- `city addtile <cityName>` takes an optional `[radius]` parameter
- `civ addtech` / `civ removetech` commands

By SomeTroglodyte:
- Use Events for moddable, floating "Tutorials"!
- Allow EmpireOverview persistence across game launches
- Moddable images for special characters

By tuvus:
- Moddable city ranges
- Extra Civ and Spy moddability