Allow mods to change homeworld starting facilities criteria

**What do you want to see?**
Allow mods to change homeworld starting facilities criteria

**How would it help players?**
Would give modders more freedom

**Alternatives**
not really, decades of se4 mods being handicapped by this design limitation proved that

**Screenshots and mockups**
naw I am good

**Things to consider**
Entirely in settings.txt?
Entirely in a new txt file and is only "activated" when that txt file is present in the mod?